WAVEELY GROUP SPECIES. 299 



Genus SCHIZODUS, King, 1844* 



(Ann. and Mag. Nat. Hist., XIV., 313.) 



ScHizoDus Medinaensis, Meek. 



Plate 15, figs, la, 6, c. 

 Schizodus Medinaensis, Meek (1871); Proceed. Acad. Nat. Sci., Philad., XXIII., 165. 



Shell of medium size, subtrigonal, moderately convex above the mid- 

 dle and cuneate below, somewhat longer than high ; anterior side rounded ; 

 basal margin somewhat straightened or slightly convex in outline along 

 the middle, rounded up regularly in front and more abruptly behind ; 

 dorsal outline sloping nearly at right angles from the beaks toward the 

 extremities, the anterior slope being more abrupt than the other ; pos- 

 terior side longer than the anterior, sloping with a more or less convex 

 or subtruncate outline above, and very narrowly rounded at the extrem- 

 ity below ; beaks rather prominent, abruptly pointed, located a little in 

 advance of the middle ; posterior umbonal slopes rather prominently 

 rounded or subangular from the beaks obliquely to the posterior basal 

 extremity. Surface nearly smooth, or only showing fine lines of growth. 



Length, 1 inch ; height, 0.82 inch ; convexity, 0.44 inch. 



This species has been supposed to be identical with, or nearly related 

 to, a New York Chemung form, which was, I believe, described by Mr. 

 Conrad under the name Nuculites Chemungensis. It certainly differs, 

 however, materially in form from that shell as figured and described by 

 Mr. Conrad in Vol. VIII. of the Journ. Acad. Nat. Sci., Philad., and 

 might with about as much propriety be identified with Western Coal 

 Measure species, ranging even up into beds referred by some to the Per- 

 mian. One of these, described by Prof. Swallow under the name Cypri- 

 cardia? Wheeleri (Trans. St. Louis Acad. Sci., Vol. II., p. 96, 1862), and 

 figured by Prof. Geinitz under the name Sthizodus obscurus, in his " Car- 

 bonformation und Dyas in Nebraska," agrees more nearly in form, but 

 differs in being decidedly more depressed, with less elevated beaks, and a 

 more truncated posterior outline. It also difiers from the shell under 



* Mr. Tate has proposed (Geol. Mag., 1868, p. 412) to change the name of this genus 

 to Axinopsis, because Schizodon had been used, in 1842, by Waterhouse, for a genus of 

 Mammals. This, however, seems entirely unnecessary, the two names, Schizodus and 

 Schizodon, although identical in meaning, are sufficiently distinct in sound and to the 

 eye to prevent confusion. Other instances of names as nearly alike being both re- 

 tained in Natural History, might be cited. 



