l8o PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



Stenocephalus Mercerat ; Ibid., p. 10. 



Tapinotherium Mercerat; Ibid., p. 17. 



Eurysodon Mercerat; Ibid., p. 18. 



Eleutherodon Mercerat; Ibid., p. 24. 



Amarorhynchus Amegh.; fenum. Synopt. de Mamm. Foss. de Patagonie; 



1894, p. 147. 



Mecorhinus Amegh.; Ibid., p. 156. 



Pseudhapalops Lydekker, in part ; Anales del Museo de La Plata ; T. Ill, 

 1894, p. 100. 



As the Megalonychidcz are to the other families of Santa Cruz Gravigrada, 

 so is Hapalops to the other genera of the Megalonychidce, incomparably 

 the most abundant and the most varied ; much more than half of all the 

 ground-sloths contained in the collections of Santa Cruz fossils are refer- 

 able to this genus. Future research may show that the formidable list 

 of synonyms should be reduced, for several of these supposed genera 

 have been established upon fragmentary and uncharacteristic types, and 

 better preserved specimens may prove that more or fewer of them are 

 entitled to generic distinction. 



There is a remarkable difference of size among the species of Hapalops, 

 ranging from some of the smallest to some of the largest contemporary 

 members of the family, and in the different species, so called, there is the 

 greatest variability in this respect, giving an almost complete series of 

 transitions from one extreme to the other. 



The dentition is fairly constant and characteristic ; the first tooth in 

 both upper and lower jaws is in the same fore-and-aft line as the other 

 teeth and is isolated by a diastema of varying length ; it is quite small, 

 caniniform and, in most instances, obliquely worn ; in shape it may be 

 cylindrical, obscurely trihedral, or laterally compressed ; - is implanted 

 near the premaxillary suture. The molariform teeth are subquadrate, 

 transversely oval, or faintly trihedral, somewhat as in Megalonyx. The 

 skull is elongate and generally narrow ; the occipital and sagittal crests 

 are never very distinct and may be entirely absent, and in almost all the 

 species the supra-occipital is reflected over upon the roof of the cranium 

 for a considerable distance. The facial part of the maxillary extends 

 beyond - as a thin plate and forms the side wall of the anterior nares, 

 without any thickening of the margin. The premaxillaries vary greatly 

 in length, but are always composed of an anterior, slender branch and two 



