294 
PALAEONTOLOGY OF NEW-YORK. 
Surface, in well preserved specimens, marked by fine close concentric 
striae, with indistinct radiating striae ; the concentric striae sometimes 
crowded together in folds or ridges. 
A gutta-percha impression from a mould of apparently the same spe¬ 
cies, and from which the natural cast, figures 27 and 28, was taken, is 
distinctly radiatingly striate, as shown in figure 30. 
The cast of the ventral valve preserves evidence of moderately strong 
teeth with dental plates reaching to the bottom of the rostral cavity, 
where they are distinctly limited. The muscular area is only moderately 
impressed, and the adductor imprints are cordiform : the surrounding 
surface is papillose above and striate below. 
In the dorsal valve the muscular imprints are elongate, situated about 
the centre of the valve, and separated by a median septum. The surface 
of the cast is more or less papillose-striate. In some of the casts the 
muscular imprints and septum are scarcely visible, but the latter, when 
entirely preserved, has extended below the middle of the length of the 
valve. 
This is a shorter and more rotund species than either of those described, and 
maintains its proportions pretty uniformly. The smallest specimen measured has 
a length of four lines and a half, and the original specimen figured ( figs. 23 - 26, 
pi. 47 ) has a length of eleven-sixteenths of an inch, with a width which is scarcely 
less, and the depth is seven-sixteenths of an inch. A single ventral valve mea¬ 
sures a little more than three-fourths of an inch in length. 
Figures 21 - 26 illustrate typical forms of this species. Figure 31 is a cast of the dorsal 
valve ; and figures 27 - 29 are dorsal, ventral and cardinal views of a well marked specimen, 
which, however, has not its characters very strongly defined on the dorsal side. 
The cast illustrating the interior characters, together with the gutta-percha 
impression from the mould of the same, have so much the general aspect and 
proportions of the A. polita that I have hesitated to separate them. All the 
original specimens of A. jpolita are more or less exfoliated, though apparently 
very nearly entire, but none of them give indications of continuous radiating strise. 
Although the striated surface is a departure from the prevailing surface characters 
of Athykis, .the cast does not present any features incompatible with a species of 
that genus. 
Geological formation and localities. This species occurs in the Chemung group 
at Jasper, Steuben county ; at Randolph and Albion, Cattaraugus county, and 
other places in this group in Southwestern New-York. 
