410 PAT AGONIAN EXPEDITIONS : PALAEONTOLOGY. 



Closely allied to Stichomys, but with grinding teeth of much more com- 

 plex pattern and comprising species which are of much smaller size than 

 those of Stichomys. Although it is one of the commoner Santa Cruz 

 rodents, this genus is still very incompletely known, and only from jaws 

 and more or less fragmentary skulls, no other part of the skeleton having 

 yet been found. 



The incisors are very delicate and have convex faces, with thickness 

 slightly exceeding width. The upper grinding teeth have a single internal 

 fold and p A is simpler than the others in having but two external folds, 

 while the molars have three such folds, which are broad and deep and of 

 V-shaped cross-section, thus producing four sharp and prominent external 

 vertical ridges. The molar pattern is thus highly complex and character- 

 istic. Each of the upper dental series is curved, with the convexity of 

 the curvature inward, so that the two rows approximate each other most 

 nearly at about the middle of their course, while the ends are more widely 

 separated. 



In the mandibular teeth the pattern is reversed, with single external 

 fold ; in p T , m T and -% there are three internal folds, while m has but 

 two, like p-. 



The resemblance of the upper teeth of Spaniomys to those of the recent 

 Kannabateomys is very close and striking, except that in the latter p A has 

 three external folds, like the molars. On the other hand, the lower teeth 

 of the modern genus, except p- f , are less complicated than those of 

 Spaniomys and are more like those of Stichomys. 



So far as it is possible to make comparisons, the skull closely resembles 

 that of Stichomys and is also much like that of the recent Echimys, though 

 the upper contour is straighter and the cranium relatively narrower. In 

 one specimen the occiput is retained, though in such a badly fractured 

 condition as to render exceedingly difficult any determination of the 

 sutures in this region. The occiput is like that of Loncheres, though 

 somewhat narrower, while the paroccipital processes are longer and are 

 attached to the largely inflated tympanic bullse. Apparently, the supra- 

 occipital has very small lateral processes, which do not extend downward 

 upon the periotics, but are separated from them by the supramastoid 

 processes of the squamosals. No sagittal crest is present and the short 

 sagittal area is defined on each side by a depression of the cranial roof, 

 producing quite a different appearance from the broadly arched and 



