IGG PROCEEDINGS OF THE ACADEMY OP 



truncated posterior outline. It also differs from the shell under 

 consideration, in being sometimes a little sinuous on the poste- 

 rior basal margin. Another Coal-measure form figured by Prof. 

 Geinitz, under the name Schizodus Rossicus, is in some respects 

 still more nearly like our shell, but differs in other characters. 



As difficult as it certainly sometimes is to separate closely 

 allied species of this genus, I cannot think that we ought to 

 refer to the same species forms found occup^nng such widely dif- 

 ferent horizons as the Chemung group of the Devonian, and the 

 Waverley group and Coal-measure of the Carboniferous; on the 

 contrary, it seems to me that we ought to regard them as distinct 

 species, although it may not be easy, in all cases, to point out 

 well-defined distinctions in the fossilized shells. 



Locality and position. Medina, Ohio. Waverley group of the 

 Lower Carboniferous. 



SCHIZODUS STJBTRIGONALIS, Meek. 



Shell trigonal-subovate, about once and a half as long as high, 

 rather convex ; basal margin more or less nearl}'- semicircular in 

 outline, rounding up regularly in front and abruptly behind ; an- 

 terior side short, rounded or subtruncate ; posterior side some- 

 what extended, rounded below, and slanting very obliquely for- 

 ward and upward above to the posterior extremity of the hinge, 

 which is short and a little straightened ; posterior umbonal slopes 

 prominently rounded ; beaks somewhat depressed and usually 

 nearer the anterior end than the middle. Surface smooth, with 

 apparently only fine lines of growth. 



Length, 0.96 inch; height, 0.66 inch; convexity, 0.36 inch. 



This species is more depressed and oblique than the last, and 

 has its beaks placed farther forward. In its depressed oblique 

 form, it agrees even more closely with S. Wheeleri, Swallow (sp.), 

 than the last, but it differs again in having its beaks placed far- 

 ther forward, or sometimes almost over the anterior margin. It 

 also appears to be alwa3's without the faint sinuosity of the pos- 

 terior basal margin sometimes seen in that Coal-measure form. 



Locality and position. Wooster, Ohio. Waverley group of the 

 Lower Carboniferous series. 



[August 15, 



