119 PALEONTOLOGY OF NEW-YOUK. 



8tri» aro of the character of S. inequistriata, S. textilis and others, a condition 

 sometimes assumed by S. perplana in the Hamilton shales of Iowa ; but we have 

 that species in the same association with this one, showing its characteristic 

 muscular impressions, with a somewhat wider area than S. mucronata, and the 

 surface striae even or raised at intervals into elongate nodes, but never having 

 the elevated striaa and equal interspaces with finer striae shown by this species. 



Although it is not always (and in some localities not often) produced at the 

 hkige-extremities, it is the only form which I can identify with Mr. Conkad's 

 description. The S. elmira is too convex on the ventral valve, and moreover rarely 

 occurs except in casts which give the strong muscular impression a prominence 

 that would not have been overlooked in the description. 



Figures 5 and 5 a, Report ( p. 266) of the 4th District of New- York, are of this species, 



and not identical with 5 6, c, which are of the S. cayuta. 

 The figure given by Mr. Vanuxem (Geol. Report of the 3d District, page 174, figure 1) 



is of this species, found in the neighborhood of Ithaca. 



Geological formation and localities. In the Chemung group, at Chemung-narrows ; 

 at the Inclined plane of the railroad near Ithaca ; near Elmira and Bath ; and 

 also at Cortlandville and many other localities in the central and southern parts 

 of the State. 



Stropliodonta Cflelata (n. s.). 



PLATE XIX. 



Shei,!- resupinate, semielliptical or semicircular ; the cardinal extremities 



extremely produced. 

 The cast shows that the ventral valve is concave, being moderately 



convex upon the umbo, and sloping gently downwards to below the 



middle ; beyond which, the anterior portion is abruptly deflected. 

 The area is of moderate width, flat and striated, with the margin crenu- 



lated for nearly its entire length ; the crenulations elongate and a 



little oblique. 



The divaricator muscular impressions form a broad flabelliform scar, 

 which is once and a half as wide as long, and has been nearly surrounded 

 by an elevated rim. Each division is marked by eight or nine distinct 

 lobes. The occlusor impressions occupy semioval spots in the upper part 

 of this area, and are separated by a narrow ridge, which becomes broader 



