CRETACEOUS FOSSILS. 389 



layer is retained on the specimens, except a little around the beaks or along 

 the hinge margins. 



Owing to these difficulties, the same that Mr. Meek has found to exist 

 among his specimens, and also to the impossibility of giving a sufficient 

 number of figures to show fully and clearly the variations which we have 

 found among the examples in hand, we shall be obliged to follow very 

 nearly the same specific limits which that author has found desirable; though 

 we must confess that in some cases we should prefer rather to consider 

 some of the forms found associated together in the same localities, and 

 presenting only slight differences, as one and the same species, than to 

 identify these far western forms with species described from Europe, as has 

 been done by so many authors. We do not dispute their great resem- 

 blances, but believe them to be rather representative species than equivalent 

 forms. 



Genus INOCERAMUS Sowerby. 

 mOCEEAMFS PEOBLEMATICUS 1 



Plate 7, fig. 11. 



Mytilites problematicus Schlot., Petrafact., p. 312. 

 Inoceramus problematicus of authors. 



The examples which we have doubtfully referred to this species, one 

 of which is figured on Plate 7, Fig. 11, are all very imperfect, and, as in the 

 case of that one, are mostly destitute of shell, being merely casts of the 

 interior surface in a yellowish sandstone; consequently the characters 

 retained are not sufficient to fully determine their specific relations. They 

 are generally more or less obliquely-quadrangular or obliquely-subovate 

 in outline, with flattened valves and rather sharp, pointed, almost terminal 

 beaks, which project but little beyond the cardinal line; the hinge line is 

 shorter than the shell below and nearly or quite at right angles to the 

 anterior or buccal border; height of the shell usually greater than the 

 length and widest below the middle of the height, the posterior border 

 gradually receding from the extremity of the cardinal line, with a slight 

 curvature, to the postero-basal angle; umbonal ridge subangular; anterior, 

 slope abrupt and rather narrow. 



