ANTHONY, FOSSIL MAMMALS FROM PORTO RICO 195 



A partially complete craniuin with all but one of the teeth^, fragments 

 of crania and rami and fragments of humeri, ulnse, radii, femora, all 

 affording more or less characters, of a large hystricomorph rodent of a 

 genus seemingly distinct from the above. 



A quite complete cranium with one mandibular ramus of a smaller 

 hystricomorph rodent. 



The anterior rostral portion of a canid skull, unquestionably an intru- 

 sion. 



In addition to the above there is a small amount of uncorrelated ma- 

 terial of fragmentary nature and also skulls and limb bones of Artibeus 

 jamaicensis. 



SYSTEMATIC TEEATMENT 



New Genus op Geound Sloth 



The type of Megalocnus came from Cuba and consequently it is not so 

 surprising to discover remains of a ground sloth on Porto Eico. The 

 feature that is remarkable, however, is that the Porto Eico animal should 

 be such a widely different type of animal. With this fact in mind, i. e., 

 that Megalocnus was a massive bulky animal, while the Porto Eico sloth 

 was a much more active, less ponderous creature, I have incorporated the 

 contrast in the following name which I offer for the new form : 



Acratocnus odontrigonus ^ gen. et sp. nov. 



Type, No. 14170, Dept. .Vert. Pal., from Oueva de la Ceiba, near Utuado, 

 Porto Rico, 1915 ; collector. Dr. Franz Boas. The skull is selected as the type. 



DESCKIPTION" 



Shull (Plate X, Pigs. 1-6; Plate XI, Pig. 1).— The skull is incomplete 

 and shows only the rostrum back to the zygomatic process of the maxil- 

 laries, one upper tooth and several pieces, somewhat fragmentary, of the 

 mandibular ramus. 



The rostrum is elongate, rather wider anteriorly and is evenly convex 

 from side to side above. There are no apparent premaxillaries. The 

 canine is large, slightly curved, of decided triangular cross-section and 

 with the worn surface seemingly much as in Cholcepus. The alveolus of 

 the canine is ver}^ long and curved, reaching the plane of the posterior 

 border of the zygomatic process on the maxillary, at which point it has 

 attained a horizontal direction. A pair of very deep preorbital fossse is 



^Acratocnus: a, without; Kpan-s, robust, heavy; "ocnus" — meaning ground sloth 

 without great weight. Odontrigonus: oSoiv = 6Sois, tooth ; TpLywvos, triangular — in al- 

 lusion to the triagonal canine. 



