NATURAL SCIENCES OF PHILADELPHIA. 247 



This shell is also scarcely distinguishable from a form that has been re- 

 garded as a variety of P. subcuneata, Meek & Hayden, in the Permian and 

 Permo carboniferous beds of Kansas. Whether specifically identical with 

 this Kansas shell, (the supposed variety of P. subcunetta,) may admit of some 

 doubt ; bat it certainly differs materially from the typical form of P. subcu- 

 neata, not only in attaining a much larger size, but in its distinctly sinuous 

 instead of convex basal margin ; also in the presence of radiating postero- 

 dorsal costse. 



Locality and position. North branch Saline Creek, Gallatin County, 111-, 

 in a bed belonging to the upper Coal Measures. 



PLEUROPHORUS ? ANGULATOS, M. & W. 



Shell oblong, about twice and a half as long as high, rather convex ; car- 

 dinal and ventral margins straight and parallel, or the latter very faintly sin- 

 uous along the middle; posterior side (which is a little imperfect in our spe- 

 cimen,) apparently obliquely truncated above, and very narrowly rounded 

 below ; anterior side very short, sloping abruptly from the beaks above, and 

 abruptly rounded beneath ; hinge line very straight, rather long, but shorter 

 than the base. Beaks depressed upon a line with the dorsal outline, and 

 located very near the anterior margin ; umbonal ridge prominent and dis- 

 tinctly angular from the beaks to the posterior basal extremity. Surface of 

 internal cast, showing faint traces of two or three distant, very obscure, con- 

 centric ridges, or undulations. 



Length, - 52 inch ; height, 0-20 inch ; convexity, 0-16 inch. 



This is one of the kind of forms usually referred by palaeontologists to 

 Cypricardia, but as we very much doubt the existence of that genus, as 

 properly restricted to such types as the recent C. guinaca, Lamarck, during 

 the deposition of the palaeozoic rocks, we have concluded to refer it provis- 

 ionally to the genus Pleurophorus. Until its hinge and internal characters, 

 however, can be more clearly determined, its true relations must remain 

 doubtful. 



The most marked peculiarities of the species are its oblong form, straight 

 and parallel cardinal aud ventral margins, and distinctly angular umbonal 

 ridge. Its anterior muscular impressions seem not to be as distinct as usual 

 in the genus Pleurophorus, but this may be due to a defect in our specimen, 

 which is an internal cast. All we know of the hinge, is an impression of a 

 long, linear posterior lateral tooth, parallel to the cardinal margin, and most 

 distinct behind. This tooth appears to have been double in the left valve, 

 for the reception of a similar elongated tooth in the right. 



Locality and position. Wabash Cut-off, near New Harmony, Indiana. 



Pleurophorus costatiformis, M. & W. 



Shell elongate, suboval, moierately convex, slightly arcuate ; the dorsal 

 and ventral margins rather long and nearly parallel, the former being a little 

 concave in outline, and the latter convex ; extremities narrowly rounded. 

 Beaks small, depressed, or scarcely rising above the dorsal margin, oblique, 

 somewhat compressed, incurved, and placed very near the anterior end ; 

 lunule small, moderately deep. Surface ornamented by concentric striae of 

 growth, and a few stronger concentric ridg6S, crossed on the postero-dorsal 

 and dorsal regions, by five distinct equidistant, radiating ridges or plications, 

 extending obliqu> ly from the beaks to the posterior margin. Of these plica- 

 tions, the lowest is the most prominent, and forms the umbonal ridge ; while 

 the upper one runs parallel to the cardinul margin, aud forms the boundary 

 of the long corselet or escutcheon. (Hinge and interior unknown.) 



Length, about 1'10 inch; height, 46 inch; convexity, 0-43 inch. 



At the same time that we propose to name this as a new species, we con- 

 fess that if we had found it in Permian strata, we should have, from its 



1865.] 



