CLINTON GKOUP. 



101 



its form it resembles the Genus JNIytilvs ; and de Koninck regards the Genus Myalixa as 

 possessing characters intermediate between the Mytilus and Pterinea, and establishing a 

 natural passage from one to the other. 



Fig. 1 a. The right valve of this species somewhat compressed, and having the anterior expan- 

 sion broken off in part. 



Fi2". 1 h. The right valve of another specimen, less compressed than the preceding. 



Fig. 1 c. A specimen preserving both valves, which are partially open along the cardinal line. 

 The lower portion of both valves is broken off. 



Fig. 1 d. 'i'he left valve of the preceding specimen, compressed so that it appears much narrower 

 than its natural form. 



Position and locality. In the upper gray sandstone south of Mohawk village, Herkimer 

 county. 



497. 20. MODIOLOPSIS OVATUS ( n. sp.). 



PL. XXX. Fig. 2 a, b. 



Shell oblong ovate, greatly extended, and gradually narrowing towards the posterior ex- 

 tremity, which is rounded ; anterior extremity short, with a sinus before the beak ; cardinal 

 line arched ; umbones prominent ; surface evenly rounded and concentrically striated. 



The surface markings are obscure in the casts, only a few stronger lines of growth being 

 usually visible. The sinus before the beak is variable, being in some specimens much deeper 

 than in others. There is, however, little difficulty in distinguishing the species by the form 

 alone. 



Fig. 2 a. The left valve of a specimen of ordinary size. 



Fig. 2 b. The right valve (imperfect) of a large individual. The sinus before the beak is deeper, 

 and the extremity more produced than is usual in this species. 



Position and locality. In the gray sandstone south of Mohawk village, Herkimer county. 



49S. 21. MODIOLOPSIS SUBCiRINATUS («. sp.). 



Pl. XXX. Fig. 3 a, b, c, d, and 4 a. 



Shell elongated, somewhat rhomboid-oval ; young specimens with an obtuse carina along 

 the posterior umbonal slope, reaching to the posterior basal margin ; anterior extremity rounded ; 

 posterior extremity obliquely truncated or rounded ; base slightly arcuate ; surface marked 

 by strong concentric folds, which are scarcely conspicuous on the posterior part of the shell. 

 In older shells the carina and concentric folds become obsolete. 



The individuals figured present the prevailing characters observable in this species, which 

 appear to have been quite numerous at this epoch. It resembles the M. anodontoides of the 

 Hudson-river group, but a comparison of the two shows them to be quite distinct. The 



