80 The Ottawa Naturalist. [August 



DESCRIPTION OF A CANADIAN SPECIES OF 

 PELTOCERAS. 



BY J. F. WHIT EAVES. 



Tlie genus Peltoceras was constituted by Dr. V/aagen for 

 the reception of certain Jurassic Ammonites from Etu"ope and 

 India, that are most closely allied to Aspidoceras and Peri- 

 sphinctes. A "short diagnosis" of this genus was published in 

 November, 1871, in the fourth part of the fourth volume of the 

 Records of th.e Geological Survey of India. And, under the 

 auspices of that Survey, a much fuller description of the generic 

 characters of Peltoceras was published in 1875, in the first volume 

 of the " Jtu-assic Fauna of Kutch." In the latter publication Dr. 

 Waagen makes the following remarks: "]^.Tost essential for the 

 generic determination of the shells I place under the name of 

 Peltoceras is the form of the earlier stages of growth, which is 

 characteristic to a high degree, and varies biit very little in m^ost 

 of the species. The strong, sharp, mostly dichotome, but some- 

 times also undivided, ribs, which cover the inner ^vhorls of those 

 Ammonites, cannot be easily mistaken, and serve well to recognize 

 the genus, even in specimens wdiere other characteristics are not 

 observable. The whorls are always very little embracing, and 

 the transversal section of the latter somewhat rectangular." 

 The genus is divided into three sections, viz.: (1) The group of 

 Ammonites nmuilaris, Reinecke; (2) the group of A. Fug^enii, 

 Raspail ; and (3) the group oi A. aihleta, Phillips. 



In the summier season of 1906, Mr. D. B. Dowling found a 

 small Ammonite, w^hich seems to the writer to belong to the 

 genus Peltoceras and to the group of P. atkleta, in rocks of 

 mesozoic and presumably of Jurassic age, on the Red Deer River, 

 Alberta, at the Rocky Mountain Park. This little Anunonite is 

 not more than an inch and a quarter in its maximum diameter, 

 and represents only the early stage of growth of the shell, but 

 that, as Dr. Waagen states, is highly characteristic in the genus 

 Peltoceras. The sutures of its septa are not preserved, but the 

 outline of its transverse section, and its surface ornamentation, 

 are essentially similar, in a general wav, to those of the correspon- 

 ding stage of growth of P.athleta, as figured by d'Orbignv, under 

 the name Ammonites atkleta. on Plates 163 and 164 of the" "Atlas" 

 to the first volume of the "Terrains Jurassiques." This Canadian 

 Peltoceras, however, seems to be soecificallv distinct from 



