332 NOTES ON THE CANIDJE OF THE WHITE KIVER OLIGOCENE. 



invariably became separated from the skull on fossilizatiou. At the bottom of the fossa 

 (*. <?., when the skull is turned with its ventral surface upward) is seen the exposed 

 periotic, or petrosal, which is only partially overlapped and concealed by the tympanic. 

 Such an arrangement is far more primitive than that which is found in any other known 

 member of the canine series, and is not easy to interpret. A clue to its meaning may, 

 however, be found in the mode of development of the bulla in the recent Canidce. Here, 

 as is well-known, the structure consists of an anterior membranous and posterior carti- 

 laginous portion, which eventually ossify and coalesce into a single bulla. Reasoning 

 from this analogy, we may infer that in Daphcenus the bulla was also composed of two 

 portions, but that only the anterior chamber was ossified, the posterior one remaining 

 cartilaginous. Communication between the two chambers was provided for by the space 

 which separates the hinder edge of the anterior chamber from the petrosal. If this 

 interpretation be correct, it supplies an interesting confirmation of the results derived 

 from the ontogenetic study of the recent genera. At all events, it seems much more 

 probable that we have to do here with a primitive rather than a degenerate structure. 



The parietals are large and roof in most of the cerebral fossa ; they are much less 

 convex and strongly arched than in Cards, in correspondence with the smaller size of the 

 cerebral hemispheres, and posteriorly the depressions behind the hemispheres are much 

 larger and deeper. As already remarked, the sagittal crest varies in the different species, 

 and is much thicker and more prominent in D. vetus than in D. hartshornianus. The 

 frontals are more or less damaged in all the specimens and in none of those at my disposal 

 is it possible to determine the posterior limits of these bones, though from the position of 

 the postorbital constriction we may confidently infer that they formed a smaller proportion 

 of the cranial roof than in the modern members of the family. The supraciliary ridges are 

 feebly developed, especially in D. hartsho7-nianus, and the postorbital processes are like- 

 wise much less prominent than in most of the recent dogs; from this process a ridge de- 

 scends downward and backward to the optic foramen, which, though not prominent, is yet 

 more so than in Cams. The frontal sinuses are large and yet in spite of them the forehead 

 is nearly flat, both longitudinally and transversely, with a very shallow depression along 

 the median line. The nasal processes of the frontals are long, narrow and pointed, 

 and are separated by only a short interval from the ascending rami of the premaxillaries. 



The squamosal is of moderate size and differs only in subordinate details from that 

 of Canis. One such difference is the presence of a broad shelf-like projection, the pos- 

 terior extension of the root of the zygomatic process, which overhangs the auditory 

 meatus and is doubtless to be correlated with the lesser breadth and convexity of the 

 brain. The glenoid cavity is like that of the recent species, but has a much more 

 distinct internal boundary, due to an elevation of the scmamosal at that point. The 



