[55 PALiEONTOLOGY OF NEW-YOKK, 



The proportions of length and breadth in this specimen are greatly altered by compression, 

 tlie umbones depressed, and the length of the shell apparently increased. 



Position and locality. In the central and liigher part of the Trenton limestone at Middle- 

 ville, Herkimer, Trenton Falls, Lowville, and other places. («««<« Collection.) 



198. 2. EDMONDIAj^SUBTRUNCATA ( n. sp.). 



Vi.. XXXIV. Fig. 'J ; and Pl. XXXV. Fig. 3 a, b, c. 



Dorsal and ventral margins subparallel ; anterior extremity abruptly rounded, extending 

 a little beyond the umbo ; posterior slope straight, oblique ; umbones moderately elevated, 

 with an obtuse prominent ridge extending obliquely backwards, and becoming obsolete 

 below ; surface marked by line concentric lines. 



This species is less gibbous than the following, though it is much expanded below the 

 umbones, and the front very obtuse. A single specimen preserves a portion of the shell, 

 which is marked by fine strias upon the centre and anterior portion ; while upon the posterior 

 slope it presents a few strong subimbricating ridges, which are still marked by the striae. 

 In the casts of this species from the crystalline portions of the limestone, these ridges are 

 often preserved, while other portions are quite smooth. In such instances, there is no 

 evidence of muscular imj)ressions in any part of the specimens. 



Plato xxxiv. fig. 9. A specimen preserving a part of the shell ; from the soft limestone at Middleville. 

 Plate XXXV. fig. 3 a, b. Casts of the same in the crystalline limestone at Watertown. 



— fig. 3 c. Cast of the same, showing strong imbricating ridges towards the base. 



Position and locality. In the central or higher part of the Trenton limestone at Middle- 

 ville, and in the crystalline part of tlie rock at Watertown, (State Cvlhctiou.) 



199. 3. EDMONDIA? SUBANGULATA («. s;j.). 



Pl. XXXV. Figs. 2 a, b. 



Subelliptical, with the anterior narrowed and slightly projecting ; umbones very pro- 

 minent, subangular, with an obtusely angular elevation extending thence to the posterior 

 ventral margin ; hinge line short, deeply grooved near the margin for the insertion of the 

 ligament ; surface nearly smooth, or marked by fine stria; which become undulating ridges 

 upon the posterior slope. 



This shell has a greater proportional length than the jireceding, and there is a distinct 

 oblusely angular ridge extending from tlio umbones lUMrly to the posterior ventral margin. 

 Tlie umbones are more angular than the last, the cardinal line shorter, and the anterior 

 margin more extended. 



Fig. 2 a. Left valve of this species, b. Doisal view of a single valve. 



Position and locality. In the concretionary lower part of llic Trenton limestone at Water- 

 town, Jefferson county. testate Collection.) 



