ATHYRIS OF THE CHEMUNG GROUP. 
293 
The muscular imprints of the dorsal valve are not well preserved in 
any specimens in my collection. There is a slender longitudinal septum 
extending from the beak for one-half the length of the valve. 
This species is distinguished from the others here described by the great ine¬ 
quality of the valves, and by the lamellose strise which are not unlike those of A. 
vittcita in the Hamilton group of the west. The specimens are for the most part 
poorly preserved, and occur as single valves which arc usually partially exfoliated. 
Casts of the interior are not unfrequent, but the material is usually too coarse to 
preserve the finer markings. 
The figures 9-13 of Plate xlvii illustrate the general characters presented by this spe¬ 
cies from several localities in Allegany and Cattaraugus counties. Figure 14 is the cast of 
a small ventral valve. 
Figure 15 is the cast of an elongate form of the ventral valve. Figures 16-19 are illus¬ 
trations of the cast of a gibbous form from the arenaceous beds in Cattaraugus county. 
There may, perhaps, be some doubt whether this species will prove a true Athyris. 
Geological formation and localities. This species is known to me only in the 
Chemung group. It occurs in the Genesee valley at Philipsburgh and Rockville, 
Allegany county ; near Great-valley, Randolph and Cadiz in Cattaraugus county ; 
and at Meadville in Pennsylvania. 
Athyris ? polita. 
PLATE XLVII. 
Atrypa polita : Hall, Report on Fourth Geological Dist. N. Y. Tables of Organic Remains, No. 65, 
fig. 5. 1843. 
Shell subglobose or short ovoid, more gibbous in the upper part, with a 
distinct mesial fold and sinus. 
Ventral valve scarcely more gibbous than the dorsal, the greatest gib¬ 
bosity above the middle, flattened near the beak and at about one-third 
the length becoming depressed in an undefined sinus which expands 
and becomes deeper towards the front; beak closely incurved over 
the umbo of the opposite valve and perforated at the apex. 
Dorsal valve with its greatest gibbosity a little above the middle, and 
flattened in the centre, curving abruptly to the beak and lateral mar¬ 
gins ; a broad mesial fold becoming defined at about one-third the 
length from the apex, flattened above, and very little elevated at the 
sides. 
