148 PALEONTOLOGY. 



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

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

 Mountains, and farther west; everywhere in the Benton and Niobrara Groups. 



AECIDJE. 



Genus CUCULL^A, Lamarck. 



CucuLL^A (Trigonaeca?) obliqua. Meek. 



Plate 14, figs. 1, 1 a, 1 &. 



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, J. striatus, Mantell, for instance, has one 

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

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

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

 hinge-teeth. On the other hand, I. Cuvierii, Sowerby, frona 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 umbones thaji at the free 

 margins, it should be remembered that it is the outer prismatic layer, and not the 

 inner pearly layer, that Mr. Conrad refers to. So far as I 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 different 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 often 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 Haploscapha; but Dr. Stoliczka 

 bad i^reviously 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. Conrad has informed me that he adopts the name 

 Volviceramus, and ranges Haploscapha as a subgenus under it. 



* Sowerby's original diagnosis of this genus, read before the Linn. Soc. in 1814, and published iu 

 the Trans, of same, XIII (dated 1821, but usually cited 1822-3), was drawn up from /. Cuvierii; and 

 Parkinson, who first adopted the genus in Trans. Geol. Soc., 1821 (often cited 1819), mentioned first 

 (■p. o3) I. Cuvierii ; while Mantell, who adopted it with a generic diagnosis in Geol. Suss., 1822 described 

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

 of the genus; but, owing to the fact that Sowerby, in publishing the genus in his Min. Con., Ill (title 

 p 1821, index 1822), described under it first /. concentricns, Park., some regard that as the type. 



