19211 



NATURAL SCIENCES OF PHILADELPHIA. 



33 



The interior of a l^ft valve (Plate II, fig. 3) shows a moderately 

 deep beak cavity. The muscle scars are indistinct, but so far as 

 visible seem as in Unio. The pseudocardinal teeth are moderately 

 strong, double, nearly smooth. The single blade-like lateral tooth 

 is well developed but short, and rather widely separated from the 

 pseudocardinals. This shell was 32 or 33 mm. long. 



This is the most abundant species; remains of some 14 individuals 

 have been found. 



This species appears to be related to Unio dockumensis Simpson, 

 from the Trias of Garza County, Texas, having similar though more 

 extensive radial corrugation. That shell is about double the size 

 of pennsylvanicus. 



Diplodon borealis n. sp. Figs. 5, a, b, c. 



Three specimens represent a species resembling D. pennsylvanicus, 

 but plumper, smaller (if these are of full growth), with the beaks 

 nearer the middle, at about the anterior two-fifths of the length. 



•f.j,^j»^^ 



b c 



Fig. 5. — Diplodon borealis n. sp. 



The sculpture consists of rather widely spaced radial furrow^s, much 

 narrow^er than their intervals, which are flattened and show irregular 

 weakly festooned concentric wrinkles in places. At the anterior 

 and posterior ends the radii are finer, and have the form of corru- 

 gations. The best preserved specimen measures: 



Length 14.5 mm., alt. 8.5 mm., diam. 7.3 mm. (fig. 5a). 



Another distorted shell is 20 mm. long (fig. 5b). This is also about 

 the length of the third specimen, in which one valve is partially 

 imbedded in hard shale, and the other somewhat compressed towards 

 the base (fig. 5c). 



Locality: Gray shale. Little Conewago Creek (loc. 5). 



