NATURAL SCIENCES OP PHILADELPHIA. 165 



If Cypricardina should be found to have a differently con- 

 structed hinge, I would propose for the group of Avhicli the 

 species here described might be regarded as the type, the name 

 Synopleura^ in allusion to its very regular concentric costas or 

 laminae of growth. It is still possible, however, that this group 

 may be found too nearly allied to Cypricarclites to stand as a 

 distinct full genus ; if so, the name of the species under con- 

 sideration would have to be written Gypricardites (Synopileura) 

 carhonaria. 



Locality and position. Newark, Ohio. Lower Coal-measures. 



SCHIZODUS MEDINAENSIS, Meek. 



Shell of medium size, subtrigonal, moderately convex above 

 the middle and cuneate below, somewhat longer than high ; an- 

 terior 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 nearl}' 

 at right angles from the beaks toward the extremities, tlie ante- 

 rior slope being more abrupt than the other ; posterior side longer 

 than the anterior, sloping with a more or less convex or subtruu- 

 cate outline above, and very narrowly rounded below; beaks 

 rather prominent, 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 ex- 

 tremity. 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, de- 

 scribed 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 as much propriety be identified 

 with western Coal-measure species, ranging even up into beds 

 referred by some to the Permian. One of these, described by Prof. 

 Swallow under the name Cypricardia'^ Wlieeleri (Trans. St. Louis 

 Acad. Sci., vol. ii. p. 96, 1862), and figured by Prof Geinitz under 

 the name Schizodus o&scwrws, in his "Carbonformation und Dyas 

 in Nebraska," agrees more nearly in form, but differs in being 

 decidedly more depressed, with less elevated beaks, and a more 

 1871.] 



