84 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull.106. 



margin nearly semi- elliptical; posterior side rounded, or sometimes sub- 

 truncated, with a slightly convex outline above, and a little more prom- 

 inent and rounding into the base below; hinge of moderate length, 

 with cartilage furrows small, there being about five of them in a space 

 0.20 inch; beak very gibbous, prominent, narrowed, strongly incurved, 

 and directed a little forward, its point being immediately over the ante- 

 rior margin. Surface of internal cast smooth over the gibbous umbonal 

 region, but showing traces of small, concentric undulations below the 

 middle. (Right valve unknown.) 



" Length, 2.10 inches; height from base to hinge, 1.82 inches; height 

 to top of umbo, 2.13 inches; convexity of left valve, 0.90 inch. 



" This shell has a more prominent, attenuated, and strongly incurved 

 left beak than any other species of the Catillus group with which I am 

 acquainted, being in this respect more like many species of typical 

 Inoceramus, while its general form places it with the former section. 

 No specimens of its right valve are yet known, but it is probably much 

 less convex than the left; I know of no other species with which it is 

 liable to be confounded. 



u Locality and position. — Chippewa point, Montana; Fort Benton 

 group." 



This species is known only by the single type specimen, which is evi- 

 dently somewhat distorted by pressure. I suspect that it is only an 

 immature individual of J. umbonatus, although Prof. Meek placed it in 

 a different subgenus. 



Inoceramus undabundus M. & H. 



PI. xvi. Figs. 1 and 2. 



Inoceramus undabundus Meek &. Hayden, 1862, Proc. Acad. Nat. Sci. Phila., p. 26; 

 Meek, 1876, U. S. Geol. Sur. Terr., vol. ix, p. 60, PI. 3, Figs. 2a, b. 



The following is quoted from the revised description: 



" Shell obliquely rhombic-subo vate or subquadrate, gibbous ; anterior 

 side very short, and rounding obliquely downward into the base; pos- 

 terior basal extremity prominently rounded; posterior margin broadly 

 rounded or subtruncated ; dorsal and anterior margin diverging from 

 the beaks at an angle of about 90°; hinge short; beaks moderately 

 prominent and nearly terminal, that of the left valve rather strongly in- 

 curved and directed obliquely forward, while in the right it is straighter 

 and less elevated ; umbonal axis ranging at an angle of about 70° to 

 the hinge line. Surface of both valves (in the condition of casts) orna- 

 mented by regular, strong, subangular, concentric undulations, sepa- 

 rated by wider, rounded depressions. 



"Height from the most prominent part of the base to the hinge 

 margin, 2.90 inches; height to top of umbo, 3.36 inches; convexity of 

 left valve, 1.84 inches. 



'• The strong, subangular undulations, and gibbous, obliquely sub- 



