VERTEBRATE REMAINS, PORT KENNEDY BONE DEPOSIT. 211 



The skulls preserved show that in this genus the malar bone is vertically 

 expanded as in other Megatheriidse, and that the inferior process is not so large and 

 palmate as in other genera. This portion has been lost from the skulls found 

 elsewhere. 



The astragalus is a variable bone in this genus. In the six best preserved of 

 the collection I notice the following differences : — In two smaller, the limbs of the 

 trochlear surface, which bound the trochlear fossa, are of equal width. In four 

 larger ones the external limb is the wider. In five, the sustentacular facet is con- 

 fluent with the recurved border of the navicular; in one large one the former is 

 smaller and is widely separated from the navicular. In two large ones the ectal 

 calcaneal facet is nearly flat ; in one it is deeply decurved toward the sustentacular 

 facet ; in three others it is intermediate. These astragali belong in all probability 

 to M. wheatleyi 



The four species of Megalonyx differ as follows : 



Synopsis of Species. 

 I Canine-molars with a convexity on the internal side. 



Largest ; superior canine-molars with groove anterior to internal bulge ; long- 

 diameter about 40 mm. ; inferior canine-molar compressed ; M. jeffersonii. 



Large ; superior canine-molar without groove anterior to internal bulge : diame- 

 ter about 32 mm. ; inferior canine-molar compressed ; M. wheatleyi. 



Large ; superior canine-molar uniformly convex on the inner side, and without 

 grooves ; diameter ; 1 M. loxodon. 



Small ; superior canine-molar with strong internal bulge anterior to middle, no 

 groove in front; diameter about 25 mm.; inferior canine-molar robust, 

 especially at borders ; M. tortulus. 



Young individuals of both M. wheatleyi and M. tortulus are represented in 

 the collection. Their teeth may be recognized by their gradual increase of diameter 

 to the base, their outlines being conic frusta. On such teeth of Mylodon was pro- 

 posed the genus Ophenodon of Lund, and on those of the young Megalonyx wheat- 

 leyi I proposed to recognized a species which I called M. sphenodon, an error which 

 I subsequently corrected. M. dissimilis of Leidy was proposed on an inferior 

 canine-molar which is probably identical in form with that of M. jeffersonii (which 

 is otherwise unknown), and a superior last molar which has an oval section, while 

 in the known specimens of M. jeffersonii its section is triangular. As already 

 remarked, this tooth presents in M. wheatleyi every form intermediate between 

 these extremes, so that the supposed species M. dissimilis cannot be regarded as 

 distinct from M. jeffersonii. 



The more detailed specific characters are pointed out in the following pages. 



Megalonyx loxodon Cope, Proc. Am. Phil. Soc, 1871, p. 74, fig. 2. 



This species is represented by a single superior canine-molar contained in the 

 Wheatley collection. I have found none corresponding with it in the collection 

 made by Mr. Mercer. A second superior canine-molar which I formerly referred to 



1 Blank in MSS. 



