964 PALEONTOLOGY OF NEW- YORK. 



This shell has few distinguishing features externally, but is more inequilateral 

 and more acute posteriorly than the Trenton species referred to this genus, and 

 bears a more general resemblance to the modern Nucula. There is no cartilage-pit 

 beneath the beak, the crenulations in the cast being continuous. 

 Fig. 1. A cast of the left valve. 



Geological position and locality. In the Tentaculite limestone, Winfield, Herkimer 

 county. 



IModiulopsis ? dubius ( n. s.). 



Plate XLIX. Fia. 2 a - «. 



Shell transversely elongated, more than twice as wide as long : ventral 

 and cardinal margins nearly parallel, the base sometimes a little con- 

 cave ; umbones nearly at the anterior extremity, subacute, with an 

 obtusely angular ridge extending from the beak obliquely backwards ; 

 posterior extremit}' more or less rounded, or obliquely subtruncate. 

 Surface finely striated, and marked at intervals by stronger wrinkles of 

 growth. 



The specimens examined exhibit considerable variety in the strength of surface- 

 marking; owing, no doubt, in some measure, to the degree of exfoliation, and to 

 maceration previous to imbedding. The oblique ridge along the posterior umbonal 

 slope is often indistinct, though it exists in well-preserved specimens. In the only 

 specimen seen with the two valves in connexion, there is a distinct external liga- 

 mental area, and an ovate or cordiform escutcheon beneath the beaks in front. 



Although resembling in form some species of Orthonota, it does not present the 

 plications along the hinge-line which mark the typical species of the genus; and 

 though wanting in some of the characteristics of the Modiolopsis, I have referred 

 it with doubt to the latter genus. 



Fig. 2 a. The right valve of a specimen which is slightly imperfect at the posterior ex- 

 tremity. 



Fig. 2 6. Cardinal view of the same. ( The apparent gaping at the posterior extremity is 

 due to imperfection of the specimen.) 



Fig. 2 c. The right valve of this species. 



Fig. 2 d. The left valve of a larger individual. 



Fig. 2 e. A fragment of limestone preserving the separated valves of several individuals. 



Geotogical position and locality. In the Tentaculite limestone, Winfield, Herkimer 

 county. 



