NO. 9 MAMMALS FROM CAVES IN HAITI MILLER 2g 



(p. 175, fig. 96) ; (e) a fragment of an atlas much larger than the 

 corresponding part in Acratocnus odontrigonns or O. ( ?) comes. The 

 area of the superior articular process in this atlas is nearly four times 

 as great as that of another specimen from the same cave (the large 

 cave near St. Michel) which I refer without much hesitation to 0. ( ?) 

 comes (pi. 10, fig. i) ; (f) several foot bones and ungual phalanges 

 of more robust structure than any known in the Porto Rican Sloth. 



PAROCNUS SERUS sp. nov. 



Plate 7; plate 8, fig. 2; plate 9; plate 10, figs. 2, 3 



Type. — Right femur (lacking epiphyses) of immature individual, 

 No. 253228, U. S. Nat. Mus. Collected in large cave near St. Michel. 

 Haiti, January, 1928, by Arthur J. Poole. 



Characters. — An animal considerably larger and more heavily 

 built than Acratocnus odontrigonns or A. ( ?) comes, its weight as 

 roughly estimated by comparison of limb bones with those of pigs, 

 probably 150 lbs. or more. 



Femur. — As compared with that of Acratocnus odontrigonns the 

 femur of Parocnns serus (pi. 7) is immediately distinguishable by 

 the absence of the lesser trochanter, as well as by its greater size 

 and the much more noticeable antero-jwsterior flattening of the upper 

 portion of the shaft. In a large femur of Acratocnus (No. 177 16. 

 Amer. Mus. Nat. Hist.) the two diameters of the shaft at middle of 

 its upper half, lateral and antero-posterior, are respectively, 26 mm. 

 and 17 mm.; in the type of Parocnus tardus they are 38 mm. and 

 14.5 mm. The ratio of antero-posterior to lateral diameters is there- 

 fore about 65 in Acratocnus and only about 38 in Parocnus. At 

 middle of shaft the discrepancy is slightly less : ratio of antero- 

 posterior to lateral diameter about 61 in Acratocnus, about 45 in 

 Parocnus. Below the middle of the shaft the diameters in the two 

 femurs are essentially alike, with ratios of 58 and 59, a difference 

 which is too slight to have any special significance. 



In addition to this striking peculiarity of general form the femur 

 of Parocnus serus is further distinguished from that of the known 

 species of Acratocnus by the absence of a lesser trochanter and the 

 presence of a low ridge about 35 mm. in length extending obliquely 

 downward and backward from the middle of the neck across the 

 narrow inner aspect of the bone to its posterior margin ; by the more 

 thickened gluteal ridge; and by the presence of a noticeable con- 



