200 The American Geologist. Octobor, i.s9f> 
From />. iiifermediHs its separation is not difficult on the 
ground of size alone. The mandible, when complete, did not 
exceed six or six and a half inches in length, or less than half 
of that of the larger species. It is also much less massive, 
but in general outline the two are not unlike. The cranium 
also occurs entire, as in that species, and is figured in our di- 
agram. It shows all the plates outlined in the engraving of 
D. intennedius, given in the American Geologist for October, 
1892 (Vol. x). The two sockets on the ex-occipital plates 
for receiving the tenons of the supra-scapulas are, as usual, 
broken, it being impossible to separate these plates so long as 
both are entire. The pre-orbital plates, though imperfect, 
indicate less prominence than in the cranium of Z). interme- 
dins. The brain cavity is crushed in, the bone covering it 
being thinner than the adjoining plates. The ethmoid is de- 
tached and only one-half of it was found. The two premax- 
illse remain nearly in place, but so forced into the plate above 
them that they form prominences on the upper surface. They 
ditfer somewhat in form, perhaps in consequence of use, but 
it is worth notice that the grooves worn in the outer edge of 
the mandibles by friction differ in the same manner. The 
sensory canals are distinct, and their course may be more 
readily traced over the skull than in any other specimen yet 
figured. They are indicated by double dotted lines. 
Fragments of both suborbitals were secured, but they are 
too imperfect for figuring and present no peculiar characters. 
The maxillary tooth of the left (?) side is figured and 
shows three denticles near the point. It is almost certainly 
beveled by friction against the mandible. 
The medio-dorsal plate is small, measuring but seven and a 
half inches in extreme length (of which the narrow projecting 
stem takes up two and a half inches) by six inches in greatest 
width. It is almost perfect, as shown in the figure, but pre- 
sents no characteristic feature calling for notice. 
The supra-scapula or ante-dorso-lateral plate is remarkably 
elongate laterally and very short in the fore and aft direction. 
The well marked tenon is strengthened by a flange connecting 
its whole length witji the main plate, which shows extensive 
underlapping surfaces on its exterior aspect. Fragments of 
