CAMBEO-SILUEIAN OF MANITOBA. 77 



CEPHALOPODA. 



POTERTOCERAS NOBILE. (N. Sp.) 



(Plate XIV, fig. 1.) 



Shell very large, attaining to a length of upwards of seven inches, straight, snLtur- 

 biuate, about one third longer than broad and broadest a little in advance of the mid- 

 length, considerably inflated but slightly compressed, one side being flatter than the 

 other, so that the outline of a transverse section through the broadest part would ])e 

 nearly elliptical, and the dorso-ventral diameter about one fourth greater tluxn the lateral. 

 Septate portion increasing rather rapidly in size from the apex : body chamber rather 

 large, occupying more than one third but less than half the entire length, and narrowing 

 gradually and somewhat convexly to the aperture : characters of the aperture unknown, 

 though, as far as can be made out in the most xierfect specimen collected, it appears to 

 have been simple and entire, as well as apparently rather large and subovate in outline. 



Sutures, or outer edges of the septa, nearly straight all round, parallel, and, in the 

 specimen figured, placed at a distance of eight millimetres apart at or near the (imiierfect) 

 posterior end, while the four nearest to the body chamber appear to have been about four- 

 teen millimetres apart. In places where the test has been broken off" and the oast of the 

 interior exposed, the septa are often seen to be coarsely crenrrlated. Surface markings 

 and shape and position of the siphuucle unknown. 



Dimensions of the most perfect specimen known to the writer (in which, however, 

 about two chambers are broken off at the posterior end) : — length, 1*77 millimetres ; 

 maximum dorso-A'cntral diameter, 124 mm. ; greatest lateral diameter (approximately) 

 about 98 mm. 



East Selkirk, Manitoba, T. C. Weston, 1884: one badly preserved and somewhat 

 distorted but otherwise nearly perfect specimen, and a large fragment of another, consist- 

 ing of the greater part of the septate portion of the shell. Lower Fort Grarry, Manitoba, 

 T. 0. Weston, 1884 : one very imperfect specimen, consisting also of most of the cham- 

 bered portion of the shell. 



This species is provisionally referred to Poterioceras, on account of its supposed simple 

 and entire aperture, but it may j^rove to be a true Gomplinceras. 



The genus Poterioceras was thus originally defined by M'Coy : — " Sliell fusiform, short ; 

 mouth contracted ; siphuncle dilated between the chambers, eccentric. Distinguished 

 from the true Orthoceraliles by its short fusiform contour, and contracted mouth." This 

 diagnosis is accompanied by a small diagram, which shows that although the body 

 hamber narrows rapidly from its commencement up to the aj^erture, yet that the aperture 

 itself is simple and entire, and neither T-shaped or lobate as in Gomphoeeras, nor 

 contracted in the middle and expanded at both ends as in Phragmoceras. 



The validity of the genus Poterioceras is not recognized by Barraude, Fischer, Zittel 

 and others, who place the name among the synonyms of Gomphoeeras. On the other hand, 

 in +he first part of his Monograph of the British Fossil Cephalopoda, the Rev. Prof. 

 Blake accords full generic rank to Poterioceras on the ground that "the only species 

 described by M'Coy, as well as his diagram, indicates a genus with the form of a 

 Gomphoeeras without its peculiar aperture." In the same volume. Prof Blake contends 



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