NATURAL SCIENCES OF PHILADELPHIA. 161 



two Ayidel3'-separated horizons would doubtless show other differ- 

 ences of details. 



Its branches are narrower, and the number of its longitudinal 

 rows is less than in the species from the Corniferous limestone 

 that I have described under the name P. Gilherti^ Mdiich also 

 differs in having longitudinal ridges between the rows of pores. 



Locality and position. Newark, Ohio. Coal-measures (loAver 

 part). 



AVICULOPECTEN SANDTJSKYENSIS, Meek. 



Shell attaining a rather large size, strongly compressed, very 

 nearly equivalve, rather oblique, somewhat longer in its antero- 

 posterior diameter than high ; posterior margin rounded and 

 somewhat produced below, and sloping upward and forward 

 above ; anterior margin rounding obliquely backward and down- 

 ward from the anterior ear into the base, which is semiovate, 

 being a little more prominent behind than anteriorly ; hinge line 

 rather distinctl}'' shorter than the entire antero-posterior diame- 

 ter of the valves ; ears flat, subequal, and acutely pointed, the 

 posterior one being shorter than the margin below, and the ante- 

 rior sometimes longer than the anterior margin beneath ; in the 

 left valve both are defined by somewhat angular nearh' equal 

 marginal sinuses, while in the right valve the anterior one is 

 slightly concave and defined by a more angular sinus, from which 

 a linear impression extends obliquel}'^ upward to the beak, which 

 seems not to project above the cardinal margin ; beak of left 

 valve slightl}^ more convex than that of the other, but scarcely 

 more prominent, and placed a little in advance of the middle of 

 the hinge. Surface of left valve ornamented by numerous un- 

 equal, slender, radiating costai or thread-like lines, that are nar- 

 rower than the spaces between, and obscure concentric striae, only 

 the latter of which are usually seen on the ears ; surface of right 

 valve similarly but less distinctly marked. 



Antero-posterior diameter of a specimen under medium size, 1.27 

 inches; height, measuring at right angles to the hinge, 1.20 inches; 

 convexity, about 0.16 inch. Some specimens were, when entire, 

 evidently not less than twice the linear dimensions of that from 

 which these measurements were taken. 



As near as can be determined from Mr. Conrad's rather brief 



1871.] 



