112 CONTRIBUTIONS TO CANADIAN PALEONTOLOGY. 



of some Scaphites of the Cretaceous. Even the large and extremely 

 aged specimens of Acrochordiceras figured by Mojsisovics retain the 

 entire trachyceran pilix', and in part the tubercles or at least indica- 

 tions of them. It is very 'jvident that in this species a marked change 

 takes place either upon the transient living chambers of the adults or 

 upon the latter part of the last whorls in extreme age. It is evident, 

 also, that the changes proceeded from the umbilical shoulders out- 

 wai-d, and that the continuous piho probably entirely disappeared 

 within a short space. I did not succeed in cleaning the abdomen sat- 

 isfactorily and therefore cannot say positively that the pite or ribs 

 cross it as in Acrochordiceras. The sjioeies is ceitainly new, so far as I 

 can judge." 



Trachyceras Canadense. (N. Sp.) 

 Plate 18, figs. 4 and 4 a. 



Shell comDressed at the sides and a little the thickest around the 

 umbilical margin : periphery or abdominal region broad and flattened, 

 but rounded at its junction with the sides and encircled in the centre 

 by a deep, narrow groove or abdominal channel. Yolutions rather 

 strongly involute, the umbilicus occupying about one-fourth of the 

 entire diameter : maximum breadth of the outer whorl a little less 

 than its dorso-ventral diameter as measui-ed from the umbilical margin 

 to the outer boundary of the abdominal channel : umbilical margin 

 distinct and subangular; inner wall of the umbilicus steep. 



Surface of the outer volution marked by transvei-se ribs which are 

 ornamented by rows of closely arranged tubercles. On the inner half 

 of each side the ribs are nearl}' straight or but slightly flexuous, but 

 on the outer half they curve concavely forwards in such a way as to 

 form a scries of obtusely pointed or narrowly munded linguiform pro- 

 cesses on the periphery, in the centre of which, however, they are 

 invariably cut thi'ough by the nai'row abdominal channel. Many of 

 the ribs bifurcate from a tubercle placed on the umbilical margin, and 

 these bifurcating ribs, which extend outward to the abdominal chan- 

 nel, usually alternate with one or two simple libs of similar length. 

 On the outer half of each side, one or both of the branches of these 

 bifurcating ribs occasionally divides again, ami in other cases a short 

 rib, which itself bifurcates near or upon the abdominal region, is inter- 

 calated between the two branches. In one instance, also, a shorl, 

 bifurcating rib alternates with a similar but much longer one. On 

 each side of the peripheral or abdominal groove the longer libs, 

 whether simple or bifurcating, bear transversely elongated tubercles, 



