300 PALAEONTOLOGY OF OHIO. 



consideration, in being sometimes a little sinuous on the posterior 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 diifers in other characters. 



As difficult as it certainly sometimes is to separate closely allied. species 

 of this genus, I can not think that we ought to refer to the same species 

 forms found occupying such widely different horizons as the Chemung 

 group of the Devonian, and the Waverly group and Coal Measure of the 

 Carboniferous ; on the contrary, it seems to me that we ought generally, 

 under such circumstances, 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. Waverly group of the Lower Carboniferous. 



Genus GRAMMYSIA, DeVerneuil, 1847. 

 (Bull. Soc. Geol. Fr., IV., 2d ser., 696.) 



Grammysia? Hannibalensis, Shumard (sp.). 



Plate 16, figs. 5a, b, c. 



Allorisma Hannibalensis, Shumard (1855) ; Missouri Geological Report, Vol. I., Part II., 



p. 206, pi. C, fig. 19. 

 Grammysia Hannibalensis, Hall (1870?) ; Prelim. Notice Lamellibr. Upper Helderberg, 



etc., p. 62. 



Shell small, transversely subovate or subtrapezoidal, with anterior and 

 umbonal regions gibbous, and the height at the beaks equaling about 

 three-fifths the length ; anterior end sloping abruptly from the beaks 

 above, with a straight or slightly concave outline, to the lower end of the 

 lunule, where it narrowly rounds into the base, or is sometimes suban- 

 gular; base forming a broad semi-elliptic or semi-ovate curve ; posterior 

 extremity more compressed, apparently sometimes a little gaping, usu- 

 ally narrowly rounded in outline at the middle, and thence truncated 

 obliquely forward and ui3ward above, to the posterior extremity of the 

 hinge ; cardinal margin more or less nearly horizontal, straight, or a little 

 concave in outline, and inflected along its entire length so as to form a 

 well-defined escutcheon ; lunule generally distinctly defined, rather' deep, 

 and presenting an obovate outline ; beaks prominent, strongly incurved 

 at right angles to the hinge, so as to bring their points nearly or quite 

 in contact ; posterior umbonal slopes prominently rounded ; posterior 

 dorsal region abruptly compressed, and sometimes separated from the 



