528 S. W. WILLISTON 



two genera. Parts only of the walls of the rhinencephalic chamber 

 are preserved. 



The maxillary teeth, which extend backward to opposite the 

 beginning of the infratemporal opening, are all very small, and 

 are much more numerous than in Cacops; I count about forty-five 

 in each maxilla. Those preserved entire are scarcely more than two 

 millimeters in length. 



The mandibles, which, with the exception of the extreme anterior 

 end, are preserved complete, are, like those of Cacops, slender bones, 

 deepest immediately in front of the cotylus, with a relatively high 

 coronoid process, which fitted into the infratemporal fossa. I count 

 about thirty-five teeth in each dentary, as preserved. The external 

 surface, at least posteriorly, is closely impressed with circular or oval 

 pits, like those of the cranial table. 



Carapace. — The carapace, as preserved, is of essentially the same 

 character as that of Cacops, but of a far greater development. In the 

 series, as adjusted, there are indications of twelve or thirteen vertebrae 

 participating in the shield, and others possibly are lost. The whole 

 number may have been the same as in Cacops aspidephorus, that is, 

 fifteen, but I suspect there were more. The first dermal shield, 

 covering three or four vertebrae, appears not to have been intimately 

 associated with the spines of the vertebrae. It is very large, not 

 much broader than long, and heavy. Its front border is very obtusely 

 angular in the middle with the borders receding and rounded. The 

 lateral borders are subparallel and gently convex in outline. The 

 posterior border has a gentle emargination in the middle with the 

 lateral sides slightly convex behind. The planes of the sides have an 

 angle of nearly forty-five degrees with each other and are broadly 

 rounded in their union. The dorsal surface is rather deeply pitted, 

 the depressions rounded or oval with reticulating ridges between them. 

 The under surface is smooth, and appears not to have been underlaid 

 with lateral expansions of the spines. Back of this shield, on the 

 under side, there are nine spine dilatations, the first six or seven com- 

 plete in the specimen. They are thin, flat plates, apparently co-ossi- 

 fied with the rather slender spines above, directed nearly transversely, 

 with a less angle of declivity than has the nuchal or scapular shield. 

 The outer extremities are narrowed or obtusely pointed, their upper 



