EDENTATA OF THE SANTA CRUZ BEDS. 159 



genera is the absence of the deep V-shaped notch in the posterior border 

 of the basioccipital, which, in the present species, is represented merely by 

 a broad and very shallow emargination. The condyles, which are small 

 and of the usual semicylindrical form, are very widely separated, in corre- 

 lation with the unusual breadth of the basioccipital. The basisphenoid is 

 considerably broader than the latter at their common suture and thus the 

 fossae in the cranial floor are very much wider than usual. How far these 

 great open spaces were filled by the missing tympanics, it is impossible 

 to say, but their shape, as determined by the difference in breadth 

 between the basioccipital and basisphenoid is different from that of any 

 other Santa Cruz glyptodont. 



The cranium is rather narrow, contracting forward gradually to the 

 postorbital constriction, and then gently expanding to the forehead. The 

 upper profile of the skull, when seen in side-view, is gently convex from 

 the occipital crest to the coronal suture, and somewhat more strongly 

 convex from that suture to the end of the rostrum ; the forehead is jnuch 

 inflated by the large frontal sinuses and the profile of the rostrum, while 

 less steeply inclined than in M. Icevatus, is more so than in any of the 

 preceding genera. The parietals are large, forming most of the roof and 

 sides of the cerebral fossa ; they are perforated by several vascular foramina, 

 which, however, are neither so large nor so numerous as in the other 

 genera, nor is the surface of the bones so rugose, but, on the contrary, 

 quite smooth and dense. 



, The zygomatic arch is of about the same relative length as in Propal- 

 cBohoplophorus, but is less expanded, while the descending suborbital 

 process is rather longer, more slender and more pointed at the distal end. 



The frontals are very large proportionately ; their postorbital processes 

 are very feebly indicated, while those of the jugals are quite distinct. The 

 maxillaries have extremely short preorbital portions, but the palatine pro- 

 cesses are of the usual form. The pterygoids are narrower and less 

 rugose than those of Propalceohoplophorus. 



Attached to the skull are the first four cervical vertebrae. The atlas 

 resembles that of the last-named genus, being very broad and short ; the 

 inferior arch is slender and rod-like, and the neural arch is much more 

 extended antero-posteriorly ; there is no spine, that of the axis reaching 

 over nearly the entire width of the neural arch ; the foramina and trans- 

 verse processes are of the usual type. The compound vertebra which 



