INVERTEBRATE PALAEONTOLOGY. 1 (',1 



1 corbicula, Miihlfeldt (typical). 



Shell orbicular-subcordate, or subtrigonal ; surface generally 

 cencentrieally sulcated ; cardinal teeth not very oblique; laterals 

 distinctly cross-striated, the posterior projecting out at right angles 

 from the erect dorsal margin ; ligament prominent. — (Example as 

 already given.) 



2. veloritina, Meek. 



Shell thick, gibbous, obliquely cordate-trigonal; beaks elevated, 

 obliquely incurved, and tumid; posterior umbonal slopes very promi- 

 nently rounded: posterior dorsal margins strongly incurved: cardinal 

 teeth typical, excepting in being more oblique; lateral teeth with 

 strife very minute or obsolete, the posterior one of the left valve often 

 appearing as if merely formed by the beveled edge of the incurved 

 dorsal margin; ligament small and depressed far below the elevated 

 umbonal slopes; surface concentrically striated. — Corbicula Durkeei, 

 Meek.* 



.".. leptesthes, Meek. 



Shell transversely elongate-subovate, compressed, typically 

 extremely thin, very oblique ; beaks depressed, subanterior ; hinge- 

 plate rather wide; cardinal and lateral teeth typical, excepting that 

 the cross-striae are very obscure or obsolete and the posterior lateral 

 rather short and very remote from the cardinal, with a wide, Battened 

 space intervening-; surface concentrically striated. — Gorbicula ! fracta, 

 Meek.f 

 Conchologists familiar only with the existing species of Corbicula would, 

 in many cases at least, hesitate to admit either Veloritina or heptesthes into 

 that genus, even as marked subgenera; and I should certainly he inclined to 

 give riore importance to the peculiarities observable in these types, were it 

 not for the fact that we find, among the numerous extinct species, forms that 



* See tigs. G to 6 /, pi. l(i, Palceont. King's U. S. Geol. Survey Fortieth Parallel. Fig. 6o of this 

 plate, showing the hinge, is turned with the heal; too much upward to give a correct idea of the obliquity 

 of the cardinal teeth. 



tit is an interesting fact, that this typical species, which was originally found in a. black shale 

 over a lied ot coal, at Hallville, iu the Bitter Creek beds of Wyoming, was recently brought by Mr. 

 Haydeu from a locality 200 miles east of Denver, Colorado, on the Kansas Pacific Railroad : where it was 

 taken from a shaft, at a depth of 400 feet below the surface, from an exactly similar shale, over a bed of 

 coal: thus indicating the existence of the Hitter Creek formation far out under the plains east of the 

 Rocky Mountains, and the probable existence of a supply of good brown coal there. 



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