TRENTON LIMESTONE. 159 



203. 4. MODIOLOPSIS NASUTUS. 



Pl. XXXV. Fig. 7. 



Compare Cypricardita nasuta, Conbad, Ann. Report, 1841, p. 52. 



— — Emmons, Geol. Report, 1842, pag. 403, fig. 4, 



Elongated ; sides subparallel ; umbones scarcely elevated above the cardinal line ; 

 posterior side extended, gradually widening and rounded at the extremity ; anterior side 

 contracted and extended into an acute beak ; surface marked by concentric, elevated, and 

 subirabricating lines. 



This is probably the young of the species which appears in the Hudson-river group, 

 where it has attained a much greater magnitude. 



Position and locality. In the compact Trenton limestone, Carlisle ( Pennsylvania ) . 



204. 5. MODIOLOPSIS ARCUATUS (n.sp.). 



Pl. XXXV. Fig. 8. 



Obliquely ovate, with a broad sinus below the umbones ; an obtuse subangular ridge 

 extending from the umbones, in a somewhat curvilinear direction, to the posterior ventral 

 margin ; posterior side broadly spatulate, rounded at the extremity ; anterior extremity 

 narrow, extended ; shell thin, with fine concentric lines. 



The only specimen of this fossil which I have seen is almost entirely denuded of the 

 shell, a small portion remaining on the lower side. It has the form of an Avicula ; but 

 from its analogy with other species of this genus, I am induced to place it among them. 



Position and locality. In the shaly part of the Trenton limestone at Herkimer. 



(State Collection.) 



205. 6. MODIOLOPSIS SUBSPATULATUS ( n. sp.). 



Pl. XXXV. Figs. 9 a, b. 



Somewhat obliquely obovate, the anterior extremity narrowed and truncate ; posterior 

 extremity broadly rounded ; shell compressed ; umbones small, prominent, placed almost 

 in the direction of the longitudinal axis of the shell, and in a line with the anterior ex- 

 tremity ; cardinal line ascending rapidly from the umbones to the summit of the shell ; 

 surface marked by fine concentric lines and a few imbricating ridges ; anterior lobe of the 

 shell small ; sinus obscure ; muscular impression scarcely visible. 



This shell deviates in a great degree from the typical forms of this genus, and may, 

 perhaps, with the previous one and the two following species, constitute a distinct genus. 

 This species is distinguished from the last, by the more ascending direction of the hinge 

 line, and less extended anterior side, as well as the more rapid expansion of the shell 

 posteriorly. 



Fig. 1 a. View of the right valve of this species, b. Dorsal view of the same. 



Position and locality. In the crystalline upper part of the Trenton limestone at Water- 

 town, Jefferson county. _ { state Collection.) 



