156 PALEONTOLOGY OF NKW-YC«K. 



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

 the uinbones depressed, and the length of the shell apparently increased. . 



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

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



• 198. 2. EDMONDIAiSUBTRUNCATA ( n. sp.). 



Pi.. XXXIV. Fig. 9; 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 fine 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 stria: 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 impressions in any part of the specimens. 



Plate xxziv. 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 e. 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 the rock at Watertown. (State Collection.) 



199. 3. EDMONDIAI SUBANGULATA (». 5p.). 

 Pl. XXXV. Figs. 2 a, 6. 

 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 striae which become undulating ridges 

 upon the posterior slope. 



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

 obtusely angular ridge extending from the umbones nearly to the posterior ventral margin. 

 The 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 the Trenton limestone at Water- 

 town, Jcflerson county. (State Collection.) 



