S64 
PALAEONTOLOGY OF NEW-YORK. 
This shell has few distinguishing features externally, hut 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. 
Modiolopsis ? dwMits (n.s.). 
Plate XLIX. Fig. 2 a - e. 
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 extremity 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 b. 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. 
Geological position and locality. In the Tentaculite limestone, Winfield, Herkimer 
county. 
