9^ PALEONTOLOGY, 



sil Hill, White Pine District; also from same in the Ruby Group, Nevada. 

 Colonel Simpson hkewise brought specimens of it from latitude 39° 33' N , 

 longitude 115° 12' W., where it seems to be quite abundant in the same 

 limestone. 



L AMELLIBH ANCHI A T A, 



PTERIIDiE. 



? Genus POSIDONOMYA, Bronn. 



POSIDONOMYA? FRAGOSA, Meek. 



Plate 3, figs. 8, 8 a. 



Shell subovate, compressed, more or less oblique, very thin and fragile ; 

 hinge short and apparently varying much in its obliquity to the longer axis 

 of the valves; beaks apparently nearly terminal; posterior basal margin 

 rounded. Surface with irregular concentric undulations and striae, usually 

 most distinct on the central region, where they are often crossed by faintly- 

 defined radiating costse, which sometimes extend nearly to the posterior 

 basal margin. 



Length of one of the largest specimens seen, measuring obliquely in 

 the direction of the longer axis of the valves, 1.10 inches; breadth at right 

 angles to the same, about 0.80 inch. 



As the specimens of this shell in the collection (or at least all that 

 remains of the shell) are extremely thin and fragile, and flattened between 

 the laminae of the shale, as well as otherwise distorted, it is quite probable 

 that it may be found necessary to modify some of the characters given in 

 the above diagnosis of the species. Until better specimens can be obtained 

 for examination, its generic affinities must also remain doubtful, though I 

 am inclined to think it belongs to some genus at least allied to Posidonomijo, 

 of Bronn, and including a species I have described from the Coal-Measures 

 of Ohio under the name Posidonomya frada; which latter also occurs in 

 the Coal-Measures of Illinois. 



[As these pages are going through the press, I observe that Professor 

 Hall and Mr. Whitfield, who have prepared a supplementary report on 

 Mr. King's later collections, have referred this shell to LunuUcardium of 

 Miinster (see Am. Jour. Sci. and Arts, vol. XI, p. 479, where the name is, 



