160 PALiEONTOLOOY OP NEW'TORK. 



206. 7. MODIOLOPSIS LATUS (n. sp.). 

 Pi.. XXXV. Figs. 10 o, 4. 



Subrhoinboidal, gibbous, broadly rounded below ; umbones prominent, obtuse, not 

 incurved ; anterior side somewhat compressed and subulate, with a slight sinus in the 

 margin, extending beyond the umbones ; posterior side compressed and expanded ; surface 

 marked by close imbricating lamellae. 



This species departs somewhat from the typical form of the genus, but possessing many 

 of the essential features, I am not prepared to refer it to any other at the present time. 

 I have been unable to discover the characteristic muscular impression upon this species, 

 though I have indeed obtained no perfect casts, and it may yet be discovered. 



Fig. 10 a, b. The left valves of two specimens, showing a slight variation in form. 



Position and locality. In the upper crystalline portions of the Trenton limestone at 

 Watertown, Jefferson county. 



207. 8. MODIOLOPSIS CARINATUS (n. sp.). 

 Pu XXXV. Figs. 11 a, 6, c. 



Obliquely subovate, with an acute carina extending from the umbo to the posterior 

 ventral margin ; umbones near the anterior margin, having a depression extending from 

 thence to the base, producing a shallow sinus ; cardinal line extending little more than 

 half the length of the shell ; posterior extremity obliquely truncated ; the slope between 

 the margin of the shell and the carina occupies more than one third the entire surface ; 

 surface marked by conspicuous elevated lines, which become more prominent and coalesce 

 towards the anterior extremity. 



The anterior portion of this shell closely resembles the M.faha; but it is readily dis- 

 tinguished from that one, and all other species of the lower rocks, by the conspicuous carina 

 which marks the posterior slope. It is a rare shell, few specimens having been found. 



There is a very similar species in the Hamilton group, but it is distinguished by the less 

 prominence of the umbones, which are not so near the anterior margin, and by the two 

 sides of the shell being more nearly parallel ; the striae, also, are sharper and more 

 distinctly defined, and the posterior truncation is more nearly vertical. 



Fig. 9 a. A large specimen, with prominent umbones. 



Fig. 9 A. A smaller specimen, showing the true form of the shell more distinctly than the last 



Fig. 9 e. A smaller specimen, in which the posterior margin is less oblique. 



Position and locality. In the compact central portion of the Trenton limestone at Middlc- 

 ville. Mr. Wadleigh. 



