Section IV., 1884. [ 239 ] Trans. Eoy. Soc. Canada. 



XIV. — Description of a New Species of Ammonite from the Cretaceous Rocks of 

 Fort St. John, on the Peace River. By J. F. Whiteaves. 



(Read May 23, 1884.) 



Several specimens of an apparently nndescribed Ammonitoid shell were collected by 

 Mr. (now Dr.) A. R. C. Selwyn, in 18*75, at Fort St. John, mostly from large concretionary 

 nodnles in shales which, from their position, may possibly represent the Fort Benton G-roup 

 of the Upper Missotiri Cretaceous. The only other fossils obtained from these shales are a 

 Pecteu, an Oxytoma, one, or perhaps two, species of Inoceramus, and a cast of a Natica or 

 Luuatia, all of which are too imperfect to be specifically determined. When fonud in 

 nodules, these Ammonites occur in the condition of imperfectly preserved and much 

 flattened casts of the interior of the shell, which vary in size from one inch and a half to 

 nearly eight inches in their greatest diameter. The nodules have been split open in such 

 a way as to expose to view only one side of each cast, upon which no vestiges of the 

 sutures of the septa can be traced. 



At all stages of growth the whorls of the species now under consideration appear to 

 have been so strongly invohite that the inner ones are nearly, if not quite, covered by the 

 outer volution. The umbilicus or umbilical depression, consequently, is very small and 

 narrow, but as its boundaries are indistinctly defined, and as the specimens are generally 

 much crushed and distorted, it is diificult to estimate its proportionate width with much 

 accuracy. 



The smallest specimens are compressed at the sides and regularly ribbed, but the 

 ribs, which are somewhat flexuous, are much narrower than the broad, shallow grooves 

 between them, and each rib bears a prominent and narrowly elongated tubercle close to 

 the periphery, and at a right angle to the side of the shell. At this stage of growth the 

 characters of the central portion of ihe peri^jhery are unknown. 



Two half-grown individuals, which measure respectively four and four and a half 

 inches in their greatest diameter, though not altogether free from distortion, are much less 

 abnormally compressed than any of the others. Judging by these specimens, which are 

 almost entirely free from the matrix, and which look as if they might have been collected 

 from the bedded rock, the breadth or thickness of the shelly tube, of which the outer volution 

 is composed, must haA'^e been considerable, and nearly or quite eqiial to its dorso-ventral 

 diameter. The periphery is broadly compressed, as are also the sides, so that the outline 

 of the outer portion of the aperture is nearly square, but this may be the resirlt of a slight 

 amount of distortion, and the siphonal edge may have been regularly rounded in its nor- 

 mal condition. "With this advance in age, the ribs become converted into broad and 

 rounded, but not very flexuous, prominent and obliquely transverse, radiating folds. In 

 the smaller of the two specimens, the primary folds bifurcate widely at the umbilicus, and 

 for the most part alternate with shorter and simple intercalated plications. The points 

 at which the primary folds bifurcate are each marked by a single transversely elongated 



