266 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



the caniniform tooth, as it is in almost all other Gravigrada of the Santa 

 Cruz, but forms a rounded, massive, pillar-like alveolus for this tooth in a 

 highly characteristic manner ; the preorbital fossae are broad and on the 

 ventral side are very deep, but they do not extend to the dorsal side of 

 the rostrum and hence the constriction is much more striking when the 

 skull is seen from below. 



The mandible is very characteristic; the horizontal ramus is short and 

 deep, very thick and massive and usually the alveolus of the caniniform 

 projects outward as a prominent pillar; in front of this pillar is a deep 

 notch, which receives the upper caniniform ; the predental beak is very 

 short, but narrowing forward rapidly and terminating in a blunt point ; 

 however, there is considerable variation in the shape of this beak, even 

 in the same species ; it is depressed and but little excavated upon the dorsal 

 side and, in correlation with its shape, the symphysis is short and steep. 

 The ascending ramus is relatively better developed than in Hapalops and 

 the coronoid and angular processes are larger ; the postero-external open- 

 ing of the dental canal is at the base of the coronoid upon the horizontal 

 ramus, the usual position among the Santa Cruz Gravigrada, except in 

 most of the species of Hapalops. 



So far as it is known, the skeleton agrees very well with that of Hapa- 

 lops, differing only in details of minor importance. As the known parts 

 of the skeleton almost all belong to E. fronto, they will be described in 

 connection with that species. 



From the material that has been collected it is impossible to reach any 

 very definite conclusions as to the number of species into which Eucho- 

 Iceops should be divided. Lydekker ('94, 95) recognizes but one species 1 

 of this genus, while Ameghino has described six, to which Mercerat has 

 added two. Of these, two are quite distinct, a larger one, E. ingens, and 

 a smaller one, E. fronto ; a third species, E. externus, would undoubt- 

 edly be recognized as valid, if we could be assured that the type and only 

 known specimen were normal. Probably a fourth species, E. cnrtus, also 

 known only from the type, should be accepted, though additional material 

 is necessary to determine this point with certainty. 



The relationships of Eucholwops are not obscure ; obviously it was de- 

 rived from a common and not remote ancestor with Hapalops and has 

 become specialized by the great development of the caniniform teeth. To 



1 E. titan Lydekker is not referable to this genus, but to Prepotkerittm. 



