DERMATEMYDID.S. 



229 



sulcus runs an irregular course across the upper ends. 65 mm. above the free border, then rises 

 and does not appear on the more posterior peripherals and pvgal. 



Mr. L. M. Lambe, of the Canadian Geological Survey, describes (op. cit., p. 40) some 

 conical, rugose bones which he believes belonged on the tail of this species. 



Cope speaks of the dermal sulci as being deeply imprest. This is true of many of them, 

 especially of those of such costals as are known the anterior plastral sulci, and some others; 

 but many are extremely narrow and shallow, and are difficult to follow as they wander over 

 and among the pits and ridges of the sculpture. 



Compsemys ogmius was based on a fragment of what Cope regarded as a costal plate and 

 on a fragment of the plastron. These were never figured. They were obtained in the Judith 

 River beds by Dr. G. M. Dawson, of the British Boundary Survey, at a point along the Milk 

 River, near the boundary between Assiniboia and Alberta. These fragments are now at 

 ( )ttawa. An examination of the bone identified as part of a costal shows that it is really a part 

 of a bridge peripheral, and that it possibly belongs to Basilemys variolosa. The fragment is 

 exceedingly poor. It is only 55 mm. square and shows only a small area of the sculpture, the 

 remainder having been weathered off. Where shown, the ornamentation is obscure. The 

 piece of plastron is 93 mm. long, 35 mm. wide, and 12 mm. thick. The sculpture is nearly 

 effaced bv weathering. While these bones may belong to B. variolosa, there is too much 

 doubt regarding them to permit us to adopt for them and the last-named species the earlier 

 name ogmius. Even if ogmius were a species distinct from variolosus, it is doubtful whether 

 new materials could be identified bv means of the type. 



Cope's assignment of the species described above to the genus Compsemys is an error. 

 The sculpture of the latter is of a very different character and there were probably infra- 

 marginals. 



I K3S. 288 and 289. Basilemys sinuosa. Carapace and plastron. Xi 

 zSS. Carapace. 289. Plastron. 



Basilemys sinuosa Riggs. 



Plate 53, figs. I, 2; text-figs. 2S8, 289. 



Basilemys sinuosus, RlGGS, Pubs. Held Column. Mus., Geol. ser., II, 1906, p. 249, plates Ixxvt. Ixxvii. 



The fine specimen on which this species is founded was collected by Dr. E. S. Riggs, of 

 Field Natural History Museum, Chicago. It was secured in the Laramie deposits of Chalk 

 Buttes, near Powderville, Custer County, Montana. With it were found bones of Triceratops, 

 Trachodon, and other characteristic Laramie fossils. The shell is nearly complete. Of the 

 plastron nothing is missing, except some parts of the bridge peripherals. Of the carapace 



