CRETACEOUS FOSSILS. 405 



the hinge line. Hinge long and straight; anterior end short and obliquely 

 rounded ; posterior end longer and rounded ; base rounded or forming a 

 short semi-elliptical curve. Surface marked by concentric undulations. 

 Oblique sulcus well marked and broad. 



A single individual, which we have referred to the above-named 

 species, occurs in the collection. It is an internal cast of both valves, much 

 weathered and somewhat displaced, as well as a little imperfect posteriorly, 

 but still a well-marked species and entirely distinct from any other form. 

 It is more ventricose than we should suppose Dr. Roemer's specimen had 

 been and the concentric furrows are less strongly marked, but otherwise 

 very similar. 



Formation and locality. — Loose, on the East Fork of Beaver Creek, 

 Black Hills, probably from the Fort Pierre' Group. 



INTEGROPALLIA. 



Subgenus IDONEARCA Conrad. 



IDONEARCA SHUMARDI. 



Plate 11, figs. 8-11. 



Area (CucnUwa) shumardi M. & H.,Proc. Acad. Nat. Sci. Phil., vol. 8, p. 86. 

 Cucullcca shumardi (M. & H.), Proe. Acad. Nat. Sci. Phil., \o\. 8, p. 285. 

 Cueullcea fibrosa (M. & H.), Proc. Acad. Nat. Sci. Phil., vol. 12, p. 428. 

 Cueullcea (Idonearca) shumardi Meek, Pal. IT. S. Geol. Surv. Terr., p. 86, PL 28, fig. 

 15 ; PI. 29, fig. 4. 



Shell obscurely trapezoidal or rhombic-ovate, usually a little longer 

 than high, with strongly ventricose valves, which become almost inflated 

 on the umbones and along the rounded umbonal ridge. Beaks large, 

 inflated, moderately elevated, approximate, and slightly incurved, situated 

 a little in advance of the middle of the length; hinge line straight, from 

 half to two-thirds as long as the shell below ; hinge-plate narrow and marked 

 by three or four very oblique, nearly parallel, linear teeth on the posterior 

 end, the sides of which are finely striated vertically, and by one or two 

 similar ones on the anterior end. (The authors of the species state that 



