178 PROCEEDINGS OF THE ACADEMY OF 



The typical specimen is beautifully iiiincralized by brilliant iron 

 pyrites, and was discovered by Mr. William Gurley, of Danville, 

 Illinois, in honor of whom I have named the species. 



Locality and i^osition. From the shale over the Danville coal- 

 bed, Danville, Illinois. 



COLLECTIONS FROM MISSOURI, WYOMING, TEXAS, &c. 



AVICULOPECTEN ? WILLIAMSI, Meek. 



Shell small, subcircular, convex lenticular not oblique; hinge 

 shorter than the antero-posterior diameter of the valves; anterior 

 and posterior margins rounding regularly into the rounded base; 

 beaks a little nearer the posterior than the anterior extremity' of 

 the hinge. Right valve rather distinctly- convex, the greatest 

 convexity being in the middle; anterior ear of moderate size, 

 shorter than the anterior margin, rather acutely rounded at the 

 extremit}', compressed so as to be distinctl}'' separated from the 

 swell of the umbo, and defined from the margin below, b^^ a mode- 

 rately deep angular sinus ; posterior ear a little smaller than the 

 anterior, and, although compressed, less distinctly defined from 

 the convexity of the umbonal region, considerably shorter than 

 the posterior margin, and nearly rectangular at its extremity', but 

 with its posterior margin slightly sinuous. Left valve a little 

 more convex than the right, but otherwise similar, unless thei*e 

 is some difference in the ears, which are not known. Surface of 

 both valves smooth or only with \e.\'y fine concentric strioe, ex- 

 cepting on the anterior ear, which (at least on the right valve) 

 is marked by a few small radiating costre. (Hinge unknown.) 



Height and length, or antero-posterior diameter, each 0.53 inch; 

 length of hinge, 0.35 inch ; convexity, about 0.32 inch. 



As I have not seen the hinge of this little shell, I cannot be 

 sure whether or not it belongs to the genus Amculopecten proper. 

 Its nearl}-^ equivalve form, and slightly larger anterior ear, to- 

 gether with its rather prominent anterior margin, lead me to 

 think it Avill probably be found not to belong to that genus, when 

 all of its characters can be known. I therefore suspect that it 

 may have to be called Strehlopteria WiUiamn, as the external 

 peculiarities mentioned seem to indicate affinities to the types 

 upon which Prof. McCoy proposed to found his genus Strehlopteria. 



[August 15, 



