FOSSILS OF TEE COAL MEASriJES. 581 



SCHIZODUS (PRISCOXIA) PERELE<;A\>. M. and W. 



PI. 26, Fig. 19. 

 lu* (Prifconia) perelfgang, MEEK and WORTHES, 1870. Proceed. Acad. Xat. Sci., Phila., p. 4-2. 



SIIKLL attaining a moderately large size, ovate-subcor- 

 clate in general form, very gibbons, apparently closed all 

 around, rather thin. Anterior and posterior views pre- 

 senting a neat cordate outline. Pallial margin senii-ovate, 

 the most prominent part being in front of the middle ; an- 

 terior side very short, and rounding np abruptly from be- 

 low; posterior side narrowly rounded or subangular; hinge 

 line apparently rather short; beaks very gibbous, promi- 

 nent, pointed, and strongly incurved, so as to bring their 

 points nearly or quite in contact ; located near the anterior 

 margin ; lunule excavated, but not distinctly defined. Sur- 

 face appearing to the unassisted eye almost smooth, ex- 

 cepting very regular raised concentric striae, or small costae, 

 on the anterior part of the valves, with obscure traces of 

 smaller stria' crossing the same. Under the highest power, 

 however, that can be well used as a hand magnifier, the 

 whole surface is seen to be covered by an extremely mi- 

 nute, perfectly regular, crowded sculpturing, as if made by 

 crowded, microscopic cross-lines, entirely invisible even 

 under a good common pocket magnifier. 



Hight of a small specimen, 0.90 inch; convexity of 

 same, 0.80 inch; length, about 1.18 inches. Other imper- 

 fect specimens show that the species sometimes attained 

 three or four times the size of that from which the above 

 measurements were taken. 



Position and locality Koof of the Danville coal, No. 7 of the Illinois 

 ion, near Danville. Illinois. We are indebted to Dr. J. C. WINS- 

 LOW, of Danville, for the specimen described. 



