INVERTEBRATE PALEONTOLOGY. 393 



It is possible thai subsection i/m, ranged doubtfully under Baeulites 

 proper, and represented by the arcuate />'. incurvatus, Dujardin, should either 

 stand as a distincl subgenus, or form a subsection under Cyrtochilus. The 



opinion has been expressed that the curvature of this type is abnormal, and 

 I am nol aware whether subsequent collections of the same species have 

 warranted this conclusion or not. If the curve is merely accidental, of course 

 the species would appear to present no essential difference from the typical 

 subgenus Baeulites; but if natural and constant, and especially if the lip of 

 this shell is sinuous instead of convex in outline on the antisiphonal side, as 

 d'Orbigny's figure (Paleont. Fr., t. 1, pi. 189, i\u, 8) would seem to indicate, 

 il would be more nearly related to the Cyrtochilus, or form an intermediate 

 subgenus between that and the typical Baeulites. 



I am much inclined to believe that the section Cyrtochilus should be 

 separated generically from Baeulites proper. The direction of its aperture, 

 and the curvature of the projection of the siphonal margin of its lip are such, 

 that the head of the animal, and the other parts connected therewith, must 

 have been protruded at righl angles to the longitudinal direction of the shell, 

 instead of on a line with the same — a peculiarity that was probably accom- 

 panied by important differences in the structure and habits of the animal. 

 It will also be observed that in this type the costse are strongest on the 

 siphonal side : while, in the typical forms of Baeulites, they are most generally 

 confined to the lateral surfaces, or most strongly defined there. It is true 

 that B. Neocomiensis, d'Orbigny, which agrees in form, so far as known, 

 with the typical Baeulites, has its costae in the same way strongly defined on 

 the siphonal side, but it differs from all the other known species in having 

 only four lobes and four sinuses to each septum ; and I am not sure whether 

 d'Orbigny's figure represents its lip entire as actually seen, or as inferred 

 from the direction of the costae. Consequently, it may represent a third 

 entirely distinct section. Other species have also been described with the 

 costae strongest on the siphonal or opposite side ; but I believe they are only 

 known in the condition of fragments that do not show the nature of the 

 aperture and the outline of the lip. 



Mr. Conrad, in 1858, used the name Cycloceras in a subgeneric sense 

 under the genus Baeulites ;* and on subsequently seeing that Cycloceras had 

 been previously used for another type by McCoy, he proposed to change his 



* Jouru. Acad. Nat. Sci.. IV ', i>l. 47, lig. 5. 



50 u 



