304 PALAEONTOLOGY OF NEW-YORK. 



Surface marked by fine close concentric striae, beneath which are dis- 

 tinct radiating stria;, and the latter become more distinct on the 

 partially exfoliated surfaces. 



The cast of the ventral valve shows a large rostral cavity, with evi- 

 dences of strong teeth and extended dental plates. The muscular ai'ea is 

 narrow and elongate. In the dorsal valve, the muscular imprint reaches 

 half way from beak to base of the valve ; the septum scarcely reaches 

 60 far. 



This shell is usually readily distinguished from the other species of the Upper 

 Heldcrberg and Hamilton groups by its elongate form, which is compressed 

 and laterally expanded towards the front ; by the remarkable arcuatiou of 

 the ventral valve, and the strong angular lateral ridge which extends from a 

 little above the middle to the apex, nearly iu the same curve as the junction of 

 the valves in their anterior half 



In this feature, and iu the less incurvation of the beak, it is distinguished from 

 some varieties of M. nasuta ; and in the same manner it is distinguished from 

 M. barrisi and M. hasJdnsi, which are always proportionally shorter shells. 



The figures 2-7 illustrate the characteristic forms of this species; figures 8-10 show 

 the extreme features of the larger individuals. The extreme length is about one inch and 

 three-fourths, with a width of a little more than an inch and one-fourth. Figure 11 is the dor- 

 sal valve of a large individual which is much broader than usual in proportion to its length. 

 Figure 12 is a cardinal view of a cast of this species, showing the median septum of tho 

 dorsal valve, and cavities made by the dental lamellae of the ventral valve. 



A single specimen, figure 1, from the Schoharie grit, appears to bo of this species. 

 Geological formation and localities. This species has been chiefly obtained 

 from some loose masses of the upper part of the Corniferous limestone near 

 Williamsville, Erie county. One specimen only has beeu obtained from tho Scho- 

 harie grit, iu Schoharie county. 



Meristella banisi. 



PLATE XLIX. 

 MeritleUa barriii : Hall, Thirteenth Report on ihc State Cabinet, p. 81. 1800. 



Shell ovoid, more or less elongate and sometimes broadly ovate, gibbous : 



valves subequally convex, sinuate in front. 

 Ventral valve, gibbous in the middle, the greatest convexity a little 



above the middle of its length, and abruptly sloping to the sides, flat- 



