114 WHITEAVES ON CRETACEOUS AMMONITES 



margin, and in this respect D. affine more closely resembles the very closely allied D. 

 Parandieri, d'Orbigny, as described and figured by Pictet. This angularity of the umbi- 

 lical margin, however, does not seem to be a constant character, as in some specimens of 

 D. Beudanti from the Earlier Cretaceous of the Queen Charlotte Islands the umbilical 

 margin is angular and in others rounded. In Europe D. Beudanti is characteristic of the 

 Gault Formation, and in the Queen Charlotte Islands of deposits apparently older than 

 the Dakota Sandstone, whereas, in the valleys of the Peace and Athabasca D. affine occurs 

 in beds that are probably the equivalents of the Niobrara-Benton of the Upper Missouri 

 Section, and of the Lower or Grrey Chalk of the English geologists, the Turonien of 

 d'Orbigny, and therefore a little newer than the Dakota. 



The genus Desmoceras was constituted by Zittel in 1884 for the reception of a large 

 group of Cretaceous Ammonites which Neumayr had previously referred to Haploceras. 

 Besides the two which are described and illustrated in the present paper, six species of 

 Desmoceras from the Cretaceous rocks of Canada have been previously enumerated or 

 described by the writer, under the generic name Ammonites, Haploceras, or Placenticeras, in 

 the three parts of the first volume of " Mesozoic Fossils " or in the second part of the first 

 volume of " Contributions to Canadian Palœontology," published by the Greological 

 Survey of Canada. The following is a synopsis of the amended nomenclature of these 

 species : — 



A. From the Earlier Cretaceous of the Queen Charlotte Islands. 

 Desmoceras Perezianum. (=Ammouites Perezianus, nobis, non d'Orbigny). 



" Breweri. (= Ammonites Breweri, G-abb). 



" Beudanti. (=Ammonites Beudanti, Bronguiart). 



" planulatum. (^Ammonites planulatus, Sowerby). 



B. From the Later Cretaceous of Vancouver and adjacent islands. 

 Desmoceras Gardeni. (^Ammonites Gardeni, Bailey). 



" Newberryanum. (=Ammonites Newberryanus, Meek). 



Ammonites Billvigsii of Meek, ' from the Cretaceous rocks of the neighbourhood of 

 Bear River in the Mackenzie River district, is probably also a Desmoceras, but, as the 

 largest known specimen is only five-eighths of an inch in its maximum diameter, its 

 generic and specific affinities are uncertain. 



Ammotii/es Laperousiamis, nobis, - from the Earlier Cretaceous of the Queen Charlotte 

 Islands, which has the distant periodic arrests of growth usually characteristic of Desmo- 

 ceras, seems nevertheless to belong to the genus Silesites of Uhlig. 



Haploceras Cumshewaense, nobis, ' from the same formation and locality as A. Laperou- 

 sianus, has also periodic arrests of growth like those of Desmoceras, but it most probably 

 belongs to that section of the genus Olcosfephanus of which the Ammonites virgalus of a'ou 

 Buch is the type, and for which Pavlow has recently proposed the subgeneric name 

 Virgatites. * 



' In Hind's Rep. Assinib. and Saakatcli. Expl. Exped-, p. 184, pi. ii., figs. 4, 5 and 6. 



^ Geol. Surv. Canada, Mesoz. Fossils, vol. I., p. 39, pi. iii., fig. 3. 



» Ibid., p. 208, pi. xxiv, fig. 1. 



* Bull. Soc. Imp. Nat. Moscou, Année 1891 (1892), p. 471. 



