144 PALEONTOLOGY 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 ; dnd 

 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 muscidar 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 Chonetes fischeri ; 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 cars 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 do- 

 preesed, and sometimes apparently a little irregularly produced and eubtruncate ; 



