EDENTATA OF THE SANTA CRUZ BEDS. 65 



Tkoracotherium lagenum Mercerat ; Ibid., p. 45. 



As originally described, this species was distinguished from the preced- 

 ing one by its smaller size ; more abundant material, however, showed 

 that this supposed difference was illusory. Ameghino later defined it as 

 having a tubular rostrum, not depressed or spatulate anteriorly, and as 

 having the forward upper teeth, especially -, separated by longer inter- 

 spaces than in P. cenophorus. As many specimens show, these are con- 

 stant characters and there can be no doubt as to the propriety of separa- 

 ting the two species ; but, on the other hand, it is far from clear that the 

 names are now applied to the same species as those to which they were 

 originally given. Since this point can hardly be determined, it seems best 

 to accept Ameghino's nomenclature. 



So far as it is known, the carapace of P. lagena has scutes of size 

 and sculpture like those of P. cenophorus and, at present, no constant and 

 characteristic difference between them can be pointed out. 



The upper and lower dental series are of more nearly the same length 

 than they are in P. cznophorus and in some specimens are exactly equal 

 in this respect. - is implanted at the suture between the maxillary and 

 premaxillary, not chiefly in the latter, as it is in P. cenopliorus ; - is 

 separated from - by a longer space than in the last named species, while 

 - and ^ are also more widely separated and smaller in size. The remain- 

 ing upper teeth are much alike in the two species and the differences be- 

 tween them are hardly greater than those between individuals. 



In the skull (Plate XIII, figs. 13) the most characteristic feature of the 

 present species is the elongate, tubular rostrum, which is but slightly, or 

 not at all, broadened at the anterior end, and is thus quite different in ap- 

 pearance from the spatulate muzzle of P. cenophorus, while the whole eden- 

 tulous part of the rostrum is narrower and more elongate than in the latter. 

 In the occiput, the prominence for the vermis of the cerebellum is less 

 developed, but the nuchal ridge is distinct, dividing the dorsal fossa into 

 two pits. The mandibular symphysis is longer, the rami taper more 

 gradually and are rather more bluntly pointed at the anterior end, while 

 the edentulous dorsal border is wider, more flattened and less inclined ; 

 the constriction between the horizontal and the ascending ramus is most 

 distinct in the present species ; the angle is more prominent, the ascend- 

 ing ramus narrower and the notch between condyle and angle broader 

 and deeper than in P. robustus. 



