CRETACEOUS FOSSILS. 147 



Our figiired specimen is merely an imperfect internal cast of a right 

 valve with the xnnbonal and anterior portions broken away. 



Professor Hall seems, from his remarks in Fr(^mont's report, to liavo 

 regarded this shell as being related to I. hirolutus of Sowerby. It is, 

 however, very distinct from that species, and even belongs to a difierent 

 section of the genus, as it certainly did not have one valve very greatly 

 larger than the other, as I know from the examination of numerous 

 specimens of both valves. The specimen figured by Professor Hall, and 

 described by him as being "ilat", is, as may be readily seen by the curve 

 of the undulations, a left valve; while the corresponding valve in A. invo- 

 lutus is extremely gibbous, elevated, and involute, being almost like a spiral 

 univalve. His figure well illustrates a peculiar flattening of the uniljonal 

 region, and the greater obliquity of the undulations often seen on that i)art 

 of both valves. 



I believe the shell here described to be also the same as that on which Mr. 

 Conrad has proposed to found a new genus, Haploscapha. Since the pub- 

 lication of his descriptions, already quoted, he has informed me that he had 

 arrived at the conclusion that his proposed new genus is identical with 

 Catlllus, Brongniart; but that he still retains his name, on the ground tliat 

 the name Catillus had been previously used for Navicella, Lamarck, by 

 Hiunphrey, in 1797.* I have not had an opportunity to examine Mr. Con- 

 rad's specimens, 'but I had always supposed this shell to be an Inocemmus, 

 and, like nearly all others, had believed Catillus, Brongniart, not to be more 

 than subgenerically distinct from Inoceramus proper. If Mr. Conrad's name 

 Haploscapha should be retained, the name of the species here described 

 would probably become Inoceramus {Haploscapha) deformls. If not, it will 

 probably be Inoceramus (Catillus) dcformis.f 



* Catillus, of Humphrey, however, was published merely in a list, without any 

 diagnosis, figure, or the citation of any kuowu type, and therefore, I should think, 

 ought not to stand. 



t The principal characters that have led Mr. Conrad to separate such shells from 

 Inoceramus are, if I have correctly understood him, a kind of rolling or flexure of the 

 hinge-margin (none of our specimens are in a condition to show whether they possess 

 this character of the hinge-margin or not), the entire absence of hinge-teeth, the very 

 thin substance of the shell near the umbones, and its greater thickness at the free 

 margins. There are various types of Inocemmus, however, without hinge-teeth ; the 



