DESCRIPTIONS OF UPPER JURA FOSSILS AMMONITIN^. 425 



vary from near the umbilical shoulders to the edge of the abdomen. The 

 single costae are sometimes, although rarely, bifurcated on the abdomen 

 and occasionally one of the branches of a bifurcation may be itself bifur- 

 cated on the abdomen. In some rare cases, instead of a bifurcation of 

 the single lateral costse or of a branch of the bifurcated lateral costae, there 

 is a single separated costation on the abdomen lying between the bifur- 

 cated, or longer single costa?. 



Perlsphinctes {Ammonites) shldegatensis, sp. Whiteaves, is an allied species 

 of the same group, and the adults of the two may be more similar than 

 one would suppose from the figure given by Whiteaves,^'^ which is prob- 

 ably that of an aged specimen. In skidegoiensis, however, the interme- 

 diate single costae are confined to the abdomen, and these parts are more 

 regular. 



Perisphinctes colfaxi obviously belongs in the group of Perisijhinctes 

 hiplex, sp. Sow. (?), of the Upper Jura, and its nearest afhnes are such 

 species of Perisphinctes eupalus (?), sp. De Loriol, in " Etage Jurassique de 

 la Haute Marne " f in the Kimmeridgian and the biplex described by De 

 Loriol and Pellat in " Formations Jurassique des Environs de Boulogna- 

 Sur-Mer " X from the Portlandian. Both of these forms, which are also 

 related to biplex, have similar single costa^, although there are no such 

 marked irregularities as in this species, and the whorl was more com- 

 pressed. The center of the umbilicus is exposed in colfaxi on the cast 

 and also on the reverse, which shows a cast of a part of the exterior of 

 the shell. The surface evidently did not differ very much from the cast 

 of the interior described above, and the young was smooth for a time 

 and very discoidal, as in the hiplex group. It especially resembles the 

 3''0ung of Perisphinctes alternans, sp. Fischer von Waldheini (Pallasianus), 

 of the Kimmeridgian of Russia.§ The sutures of alternans are very close 

 to those of this species, and the single ribs are prevalent, according to 

 De Verneuil. and the form is more like that oi colfaxi than of any other 

 European form. This entirely accords with my first impression, that 

 the nearest affines of this species existed in the fauna of the Upper Jura 

 of Russia. The same is also true of skidegatensis, the young of which, as 

 figured by Whiteaves, appears to be almost identical with specimens of 

 alternans (in the Museum of Comparative Zoology) from Russia, which 

 do not have single ribs. 



Gabb knew that this fossil was probably Jurassic, but was in error in 

 supposing that it indicated the presence of the Lias near Collax. 



*GeoI. Survey ot Canada, Mesozoie Fossils, vol. i, pt. i, pi. 7. 



j Mem. SoG. Lin. de Norm., xvi. 



X Mem. Soc. Phys. et D'Hist. Nat. de Geneve, xxiii. 



g De Verneuil : Russia and the Ural Mts., p. 427, pi. 32, fie;s. 1-3, and Orytogr. du Gouv. Mos. 



