old Aviculopectens do to our modern Pectens. For, in the modern types of the Pectenido and Aviculide, the cartilage is mainly or entirely confined to a pit or depression under or near the beaks, while, as already explained, in the Paleozoic Pterinias and Aviculopectens, we observe no such pit or depression, the cartilage being apparently attached by a series of linear furrows in a more or less wide, flattened, cardinal area, much as in the Arcida. This similarity in the arrangement of the cartilage of Aviculopecten, to what we see in Pterinia, Myalina, and some of the other groups here placed as a section of the family Pterida (=Aviculidae), together with the somewhat produced posterior ear of some of the Aviculopectens, would have led the writer to concur with Prof. McCoy, Mr. Woodward and others, in referring that genus also to the Aviculide, had it not been for the fact, that, on subjecting sections of a typical Carboniferous species (Aviculopecten amplus Meek & Worthen) to a microscopical examination, it was found not to possess the prismatic structure of the Aviculido, but the peculiar corrugated tabular structure of the Pectenido. From this fact, as well as the less oblique and more Pectenoid form of the Aviculopectens, we can scarcely doubt the propriety of including them, with probably several undescribed Paleozoic genera, as a section or subfamily of the Pectenido, parallel to the ancient Pterinia group in the Aviculidæ.

Amongst the genera here included provisionally in the group Pteriniina, the new name Gryphorhynchus will be observed. This is proposed for the reception of a group of small Triassic shells, of which Avicula gryphæata of Munster is the type, (see Goldf. Petref. Germ., ii, p. 127, pl. cxvi, fig. 10, a, b, c, d, e, f, g). This genus may be briefly characterized as follows:

Genus GRYPHORHYNCHUS, Meek.-Shell small, thick, nearly or quite as wide as long, very slightly oblique, plano-convex, or sub-hemispherical, the right valve being flat or concave, and the left very gibbous; posterior and anterior margins, somewhat sinuous, but neither valve with a defined byssal sinus. Beaks sub-central; that of the left valve elevated, gibbous, strongly incurved, and at the extremity directed obliquely forward; beak of right valve truncated so as not to be distinct from the cardinal margin. Hinge line equalling the greatest length of the shell, ranging more or less nearly at right angles to the umbonal axis; in both valves provided with a wide, well defined cardinal area. Ears subequal, not produced, concave in the right valve, and convex in the left, in which latter the anterior one is separated from the swell of the umbo by a deep oblique sufcus. Surface with fine, sometimes decussating striæ. Hinge with sev. eral small irregular teeth near the middle.

• The same relations are also observed between nearly or quite all of the Paleozoic Nuculas, so-called, and the true Nuculas of our modern seas.

This genus includes G. gryphæatus and G. tenuistriatus (= Avicula gryphæata and A. tenuistriata, of Munster, Goldf. Petref. Germ., ii, 127-8).

In the same group may also be placed, as the type of a distinct subgenus, another little Triassic species described by Munster as Avicula decussata (Goldf. Petref. Germ. ii, 128, cxvi, 12 a, b). For this form I would propose the subgeneric name Actinophorus. It agrees with the typical species in all essential characters, excepting in being much more oblique, in having its posterior margin truncated at right angles to the hinge, instead of being slightly sinuous; and particularly in having the left valve ornamented with strongly elevated, distant, radiating costæ or pli

cations.

I have not been able to see the prismatic structure in either of these types, but, from all analogy, I should suppose it could be detected in specimens in a better state of preservation. So far as known to the writer, this genus has not been discovered in America, and has only been found in the St. Cassian deposits of the Tyrol.

Under the Aviculine or Pteriina, it will also be observed that a new generic name, Eumicrotis, has been introduced. This is proposed for a well known type sometimes referred to Avicula, sometimes to Pecten, sometimes to Monotis, and by others to Aucella. Its type is Monotis Hawni Meek & Hayden, from the Permian rocks of Kansas. It also includes the closely allied European Eumicrotis speluncaria, (= Gryphites speluncaria, of. Schlotheim, Monotis speluncaria of King and others); also E. radialis (Pecten radialis Phillips); and E. Garforthensis, (=Monotis Garforthensis King). This genus may be described as follows:

Genus EUMICROTIS, Meek.-Shell more or less orbicular, planoconvex, the left valve being usually very convex, and the right flat or a little concave; not distinctly auriculate, the ears being nearly obsolete. Beaks subcentral, very slightly oblique, unequal, that of the left valve often elevated, gibbous and incurved; the other very small, and scarcely projecting above the hinge line. Hinge short, narrow edentulous. Byssal notch, or sinus of right valve, narrow, deep, sharply defined and separated from the hinge line by a small rudimentary ear, which does not project beyond the anterior margin of the valve. Scar of adductor muscle large and subcentral, those of the retractors small and placed near the beaks. Surface generally with radiating, vaulted, scaly coste, much more strongly marked on the left than on the right valve.

The species of this genus have been usually referred to Bronn's genus Monotis. A careful comparison, however, of our Kansas specimens of the species described by the author in con

nection with Dr. Hayden, under the name Monotis Hawni, with authentic European specimens of the type of Bronn's genus, (Monotis salinarius) now in the collection of the Smithsonian Institution, has satisfied me that they ought not to be placed in the same genus. In the first place, the type of Monotis is an obliquely oval, compressed, very nearly equivalve shell, with depressed, subequal beaks, presenting altogether a marked contrast with the general physiognomy of the shells belonging to the Permian and Carboniferous group under consideration. The most important difference, however, is the total absence of any traces of a byssal sinus in the anterior margin of either valve of the typical Monotis, the anterior margins of both valves being smooth, rounded, and without even the most obscure indication of an emargination, to represent the deep, sharply defined, byssal sinus of Eumicrotis.

I know nothing of the hinge, or of the microscopical structure, of Monotis salinarius, the specimens at the Smithsonian Institution being firmly imbedded in the very hard brittle matrix, and not in a condition to show any traces of minute structure. Dr. Carpenter, however, has examined a species-Avicula cygnipes, of Phillips-(which is unknown to the writer), supposed to be congeneric with the type of Bronn's genus, and finds it to possess the structure of the Pectenida, rather than that of the Aviculida. On examining thin sections of our Kansas shell, the type of the genus here described, by the aid of a magnifying • power of about three hundred and fifty diameters, the prismatic structure of the Aviculidæ is distinctly visible.

Prof. McCoy was evidently much nearer right when he referred the European species of this group to Count Keyserling's Jurassic genus Aucella, than those who identified them with Bronn's genus Monotis. Aucella, however, although more nearly allied, was founded upon a distinct group of oblique, gibbous shells, all of which are destitute of radiating costæ or striæ, but ornamented with concentric undulations, giving them much the general appearance of some species of Inoceramus. They also have a small peculiar concave ear just in front of the beak of the left as well as of the right valve, formed by the inflection of the margin of the valve, unlike anything we see in the left valve of Eumicrotis. Count Keyserling's figures and description also show that the scar of the adductor muscle is placed much nearer the ventral margin in Aucella than in Eumicrotis. Aucella would therefore seem to bear similar relations to Eumicrotis, that Posidonomya does to Monotis proper, as typified by M. salinarius.

It is remarkable that, even in late European publications, we see the so-called Monotis speluncaria placed in the genus Avicula. There is still another small group of Jurassic shells represented by one species in our collection from the far West, for which I

had thought a subgeneric name should be proposed. Farther comparisons, however, with specimens of some European species of this type, have led to the conclusion that these little shells form a section of the genus Eumicrotis, probably too closely connected by some intermediate forms to merit a distinct subgeneric name. The western species of this section alluded to above is Avicula? curta Hall, (custa, typ. err., Stansbury's Report, Expl. Great Salt Lake, 412, pl. ii, fig. 1, a, b.) This section also includes the very closely allied European species Monotis substriata Munster: also M. decussata, and M. Alberti Munster, (Goldf. Petref. Germ., ii, p. 138-9,) as well as a species figured by Goldfuss as Monotis echinati, (id., pl. cxxi, 6.)

These shells have much the general outline of the typical species of Eumicrotis, being short or suborbicular and but very slightly oblique, without any anterior ear, and generally having the posterior ear much abbreviated. They differ, however, in being smaller as well as more nearly equivalve shells, and in having the beak of the left valve much less prominent. Their valves are also destitute of an oblique sulcus often seen extending down the posterior side of the typical forms of Eumicrotis, and have a more regular appearance. They have generally a merely striated surface, and a very sharply defined byssal sinus near the beak of the right valve; in some of the species, however, the left valve has small radiating scaly ribs.

The structure of E. (Avicula) curta Hall sp., as seen by transmitted light under a high magnifying power, is finely prismatic.

In conclusion, I would remark that the numerous widely dif ferent types from the older rocks, figured in the various works on Paleontology under the names Avicula, Pecten, &c., show that much has yet to be done in classifying these shells, and that it will be necessary to establish a number of new genera for their proper distribution. I would also call the attention of paleontologists to the valuable assistance to be derived, at least in many cases, from microscopical examinations, in determining the family affinities of the ancient fossil genera of Aviculida, Arcida and Pectenida; especially, where the condition of the specimens under investigation is such as to prevent the nature of the hinge and interior from being determined. How far, however, the different types of structure may have been constant, amongst all the ancient genera of these families, remains to be determined by the examination of a larger number of species.

7 The figures here referred to are not recognizable, but we know our shell to be the same, from comparing our specimens with the type of that species, collected at the same locality.

ART. XXI.-On some Minerals of the Chlorite Group; by JoHN B. PEARSE.

THE diversities of color among the varieties of the mineral species are in many cases still unexplained. A case of this kind occurs in the so-called kämmererite, from Lancaster county, Pa., of which there are three kinds-one colored pure green, a second red and green, while the third is of a pure red. The following investigation was undertaken to determine, if possible, the cause of this variation; and as the results have proved interesting, they have been further discussed in their general relations.

The mineral is in distinct crystals. There is the strongest evidence that all belong to the trimetric system, closely resembling many specimens of chlorite and some crystals of clinochlore. They are usually hexagonal in form, rising from their base as a truncated pyramid, but the lateral surfaces are so striated as to be incapable of measurement. The pyramid is made up of a pile of crystalline plates, with their slightly projecting edges manifestly replaced, indicating a dome and an octahedron.

The three varieties are well defined, the color of the first being a pure green, sometimes a rich emerald-green, while that of the second varies considerably between these two tints, being sometimes of a pure white; and that of the third is red, with an occasional tinge of reddish-white. In the second, the colors are confined to the laminæ, instead of mixing and giving a medium tinge. The third was also dichroic in the direction of the planes of its axes, being red in the direction of its shorter lateral axis, but of a violet-blue or hyacinth in that of the longer axis.

The hardness of the green and red is 2.75; the specific gravity of the green at 64° Fahr. 2:355, that of the red 2.383, which is perhaps a little too low, as it was impossible to free the crystals of a few minute bubbles of air. They consist of flexible micaceous plates, with a vitreous lustre, and white streak. Their blowpipe reactions show the presence of chrome, and silica, the absence of manganese in both, and the absence of fluorine in the green. Traces of the alkalies were shown in the red. Both the green and red are soluble in sulphuric acid with separation of silica, but are not acted on by chlorhydric acid. The purplish green not being obtained in sufficient quantity is not included in this description. This deficiency however proved unimportant, as the analysis showed its identity with the red.

Extreme care was taken in selecting the material for analysis. Fresh and perfect crystals were used for each analysis of the same variety, in order to certify undeniably the composition.

AM. JOUR. SCI.-SECOND SERIES, VOL. XXXVII, No. 110.-MARCH, 1864.