DERMATEMYDID&. 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 pygal. 
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 
Ottawa. 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 §5 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 1s g3 mm. long, 35 mm. wide, and 12 mm. thick. The sculpture is nearly 
effaced by 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 varvolosus, it is doubtful whether 
new materials could be identified by 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. 
Fics. 288 anp 289.—Bastlemys stnuosa. Carapace and plastron. 1). 
288. Carapace. 289. Plastron. 
Basilemys sinuosa Riggs. 
Plate 33, figs. 1, 2; text-figs. 288, 289. 
Basilemys sinuosus, Riccs, Pubs. Field Columb. Mus., Geol. ser., 11, 1906, p. 249, plates Ixxvi, Ixxvu. 
The fine specimen on which this species is founded was collected by Dr. E. S. Riggs, ot 
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 
