Dr. Harla?i > s New Fossil Mammalia. 343 



Mylodon. Every experienced naturalist has felt the difficulty 

 of obtaining an exclusively descriptive name for a new genus, 

 and has acknowledged virtually the necessity of being content 

 with a partially descriptive one, if it be euphonious and not ses- 

 quipedalian. I must however here remark, that the practice of 

 proposing a name for an undiscovered future probable or possible 

 genus is questionable, and certainly hazardous. It is true, that 

 the danger of the inapplicability of such name will be dimin- 

 ished in the ratio of the extent of choice submitted by the anti- 

 cipator to the future discoverer. Dr. Harlan has left but two 

 names for the choice of the discoverer of the generic characters 

 of his Megalonyx laqueatus, and, as only a single tooth of that 

 species has been described, the names Aulaxodon and Pleurodon 

 may prove as inapplicable to the entire dentition, as they would 

 have been if either of them had been transferred from their posi- 

 tion as synonyms of Megalonyx laqueatus, to the distinct ge- 

 nus Mylodon. I may however state, that the additional expe- 

 rience which I have had of the fossil remains of Megatherioid 

 Edentata, has confirmed my belief, that the Megalonyx laquea- 

 tus of Dr. Harlan is a true Megalonyx, nor can I perceive any 

 reasonable ground for its specific distinction from the Megalonyx 

 Jeffersonii. The broken tooth (Plate XIII, figs. 7, 8, 9, Medical 

 and Physical Researches) affords none, since its relative length, 

 as entire, to its transverse or antero-posterior diameters cannot be 

 known. The Megalonyx agrees with the Megatherium and 

 differs from the Mylodon, in the greater relative length of the 

 humerus, in the greater degree of convexity of the head of the 

 bone, in the greater convexity of the articular surface for the 

 ulna ; the Megalonyx differs from both Megatherium and My- 

 lodon, in the perforation of the inner condyle of its humerus. 

 The Megalonyx agrees with Megatherium and differs from Mylo- 

 don, in the convexity of the proximal articulation of the tibia pre- 

 sented to the external condyle : it differs from both Megatherium 

 and Megalonyx, in having both the condyloid articular surfaces 

 of the femur distinct from the rotular surface. 



So well marked is the distinction of Mylodon from Megalonyx, 

 whether the bones of the latter genus be described under the 

 names Jeffersonii or laqueatus, that the generic characters, first 

 detected by me in the lower jaw of the Mylodon, are repeated in 

 most of the bones of the skeleton. They have consequently 

 been recognized by Dr. Harlan himself, when presented to his 



