148 rAL.KONTOLOGY. 



Locality and position. — Common in Kansas, and near Pueblo and Col- 

 orado City, as well as at other places in Colorado along eastern base of Rocky 

 Mduiitiiins, and lartlior went; everywhere in the llenton and Niobrara Gronps. 



AllCIDiE. 



Genus CUCULL^A, Lamarck. 

 CucuLL^KA (Trigonakoa^) OBLiQUA, Meek. 



Pla(« 1-1, fij;s. 1, 1 «, 1 h. 



Shell attaining about a medium size, rhombic-subovate, moderately 

 convex, the greatest convexity being along the posterior umbonal slope, 



presence of one or more obscure anterior teeth being an exceptional, and not by any 

 means a general, character in this group. I. striatns, Mantell, for instance, has one 

 obscure anterior hinge-tooth in one valve, while the nearly allied I. mbstriatiis is figured 

 by Goldfuss without any traces whatever of such tooth. Again, Goldfuss figures 

 another shell that he refers to J. Brongniarti, with indications of three small anterior 

 hinge-teeth. On the other hand, I. Guvierii, Sowerby, from which the original figures 

 and description of the genus were prepared, has no hinge-teeth;* and, according to 

 the best authorities, this is the case with nearly all the other known si;ecies the hinges 

 of which have been seen. 



In regard to the greater thinness of the shell at the umboncs than at the free 

 margins, it should be remembered that it is the outer prismatic layer, and uot the 

 inner pearly layer, that Mr. Conrad refers to. So far as 1 have been able to see, how- 

 ever, this outer layer is not unfrequently thinnest near the umbones, excepting under 

 the beaks along the hinge, in diti'ereut types of the genus. In our shell, this outer 

 fibrous layer, like that of other species in the lower divisions of the Upper Missouri 

 Cretaceous, is nearly always found with the inner pearly layer dissolved away, in 

 which condition the fibrous part appears to have been flexible, as I have ofteu seen it 

 abruptly folded upon itself in various ways. The rolling-over of the hinge-margin in 

 Mr. Conrad's type I should think not of generic importance. Mr. Conrad thinks 

 I. involutus of Sowerby has the hinge-characters of his Hajtloscapka ; but Dr. Stoliczka 

 had previously proposed for that type the name Volviceramus as a subgenus under 

 Inoceramus, in which genus all authorities have plased it. 



Since writing the above, Mr. Courad has informed me that he adopts the name 

 Volviccranms, and ranges Huploscapha as a subgenus under it. 



* Sowerb^i's original diagnosis of this geuiis, iv.-id before the Linn. Soc. in Ibl-I, and pnbliKlu'd iu 

 the Trans, of same, XIII (d.atcd 18'^1, but nsually cited lS22-;i), was drawn uj) from /. Cmicrii; and 

 Parkinson, who first adopted the genus iu Trans. Geol. Soc., 1S2I (ofteu cited 1819), mentioned first 

 (p. 53) /. Cuiiieni; while Mantell, who adopted it with a generic diagnosis in Geol. Suss., 1823 described 

 under it first a species referred by him to /. Cuvietii. Hence this species has been cited as the type 

 of the genus; but, owing to the fact that Sowerby, iu iiublishing the geuus iu his Min. Con., Ill (title 

 y 1821, iudex 1822), described under it first /. conccnlriciis, Park., some regard that as the typo. 



