Reviews — J. F. Whiteaves — Fossils of Manitoba. 135 



Maclurea Manitobensis. 

 Poterioceras nob He. 



,, apertum. 



Oncoceras magnum. 



Oncoceras gibbosum. 

 Cgrtoceras Manitobensis. 

 Ti ochoccras McCharlesi. 

 Apsidoceras insigne. 



Maclurea Manitobensis is of very large size, attaining a maximum 

 diameter of eight inches and a half. It is said to be more nearly 

 related to the M. Bigsbi/iof Hall, from the Trenton Group of Southern 

 Wisconsin, and to the M. cuneata of R. P. Whitfield, from the Galena 

 Limestone of the same State, than to either M. magna, Hall, or 

 M. Logani, Salter. 



To the genus Poterioceras two species are assigned — P. nobile and 

 P. apertum; the first of these is referred provisionally to this genus 

 " on account of its supposed simple and entire aperture," " but," 

 adds the author, " it may prove to be a true Gomphoceras." 



Mr. Whiteaves disagrees with Prof. Blake's view that Oncoceras, 

 Hall, is synonymous with Poterioceras, M'Coy, and observes that the 

 latter name " will probably have to be restricted to those straight, 

 Gomphoceras-\ike shells in which the aperture is simple and entire" ; 

 in Oncoceras, on the other hand, " the shell is always distinctly 

 curved and inflated in a peculiar manner in advance of the mid- 

 length, while its body-chamber is transversely constricted just be- 

 hind the aperture." It is thus seen that Mr. Whiteaves' contention 

 in favour of the distinctness of Poterioceras and Oncoceras rests 

 upon the assumption that the latter has a curved and inflated shell, 

 and the former a straight, Gomphoceras- like shell. The constriction 

 near the aperture can scarcely be reckoned as a distinctive generic 

 character, because it is met with also in some species of Orthoceras. 

 With regard to the inflation of the shell, that is a character common 

 to both forms, as is admitted for Poterioceras in the expression 

 " Gomphoceras-like " ; and as to curvature, abundant proof exists that 

 Poterioceras has a slightly but quite distinctly curved shell ; this 

 is seen in numerous specimens from the typical locality — Kildare-, 

 Ireland — whence M'Coy obtained the material upon which he con- 

 structed his genus. Thei'e therefore appears to be very little ground 

 for separating Poterioceras from Oncoceras. 



On looking at the figure of Poterioceras nobile, one is indeed struck 

 with its ' Gomphoceras-Wke aspect, and the doubt expressed by the 

 author as to whether it is really a Poterioceras will probably be 

 shared in by most palaeontologists who examine it in the light of the 

 more recent researches in these fossils. 



The uncertainty regarding the oral characters of such forms as 

 these leaves room for considerable diversity of opinion as to the 

 genus to which they belong, but our experience so far is opposed to 

 their i*eference to the genus Gomphoceras, no fossil having yet been 

 found below the Upper Silurian in which the complex, lobed aperture, 

 characteristic of Gomphoceras, is preserved. This important structure 

 being unfortunately absent in Mr. Whiteaves' specimens, the latter do 

 not help us to settle the question of the range in time of Gomphoceras. 



The species named Cyrtoceras Manitobensis is a very aberrant 

 form of this genus, if indeed it really belongs to it, the presence of 

 longitudinal to the entire exclusion of transverse ornaments being a 

 feature hitherto unknown in other species of the genus. A. H. F. 



