144 
PALAEONTOLOGY OF NEW-YORK. 
The cast of the ventral valve shows a sub-linear or low angular area, 
with a narrow foramen which has been covered by a pseudo-deltidium. 
The apex is bilobed, and there are cavities made by the teeth; and 
proceeding a little obliquely from these are gradually decreasing grooves 
diverging a little from the hinge-line, indicating an oblique ridge in the 
shell. From the outer extremity of these marks, a curving line parallel 
to the lateral margins of the shell indicates the limits of vascular impres¬ 
sions. The occlusor muscular imprints are two narrow elongate subtri- 
angular or semioval scars, and directly below are some minute vascular 
markings which separate the wide flabelliform divaricator muscular im¬ 
pressions : these are faintly striate, and, when well preserved, are dis¬ 
tinctly lobed, though usually not well defined on the exterior limits. The 
entire surface is striato-punctate. 
The interior of a dorsal valve retaining the shell is papillose, becoming 
punctate on exfoliation, and showing pustules on the anterior margin. 
The impression of the exterior sometimes shows a truncate apex and 
the imprint of a cardinal process which is bilobed, and each division 
again divided (as shown in the figure). 
A cast made from a mould of the interior of the dorsal valve (fig. 00) 
shows a slender median septum, which terminates in the cardinal pro¬ 
cess (the two principal lobes only being shown in that view). From near 
the base of the process on each side proceed the reniform vascular 
markings. The occlusor muscular imprints are minute elevations on each 
side of the median septum. The entire inner surface is striato-punctate. 
The larger specimens are usually moderately convex; but some smaller 
ones are rather gibbous, possessing otherwise the characters of the larger 
individuals. 
This species has the general form and proportions of Chonetesfischeri; but is 
distinguished by the broadly truncate apex, the wrinkles on the ventral and dor¬ 
sal valves, and more especially by the presence of spines on the ears and upon 
the body of the shell : it has likewise a more distinct area on the ventral valve. 
The C. fischeri has the apex of the ventral valve often somewhat unequally de¬ 
pressed, and sometimes apparently a little irregularly produced and sub truncate; 
