EDENTATA OF THE SANTA CRUZ BEDS. 145 



MEASUREMENTS. 



No. 15,791. No. 



Cranium, length to rim of orbit .............................. 116 .112 



" width at postorbital constriction ..................... 042 .043 



" greatest width across zygomata ..................... - . 1 20 



Occiput, height ........................................... 033 



" width at base ..................................... 066 .064 



Zygomatic arch, breadth (vertical) behind postorbital process. . . . - .025 



Rostrum, width at base .................................... 050 .05 1 



Palate, width at 1 ......................................... 020 



" " "A ......................................... 025 .025 



COCHLOPS DEBILIS Ameghino. 



(Plate XXI, Fig. 5 ; XXIV, Fig. 15 ; XXVIII, Figs. 3, 4.) 



Cochlops debilis Amegh. ; Rev. Argent, de Hist. Nat, T. I, 1891, p. 326. 



The type of this species is the right mandibular ramus of a rather young 

 individual. Ameghino's original diagnosis of it as follows: "Is distin- 

 guished by its smaller size and more slender form ; the anterior part of 

 the symphysis shows small alveoli for rudimentary incisors ; length of the 

 inferior dental series, 91 mm." (he. cit.\ 



To this species I refer a skull, unfortunately lacking the mandible 

 (Princeton collection, No. 15,592) which was found by Mr. Peterson at 

 Corriken Aike. The almost complete cephalic shield which is attached to 

 the skull makes it plain that this individual is not referable to Propalceo- 

 hoplophorus, and the teeth display the characteristic features of Cochlops 

 in a preeminent degree, while the relative narrowness of these teeth makes 

 the reference to C. debilis altogether probable. 



The cephalic shield (Plate XXI, fig. 5) has already been described in 

 connection with the account of the genus and, as this structure is almost 

 unknown in C. muricattis, its specific characteristics are not yet determin- 

 able. 



The first upper tooth is so badly broken that no description can be 

 given. The second is a little larger than in C. muricatus and has two 

 rather more distinct vertical grooves on the inner side ; a also is more 

 distinctly lobate than in the preceding species, the single external and two 

 internal grooves being decidedly deeper ; - differs from that of C. muri- 

 catus merely in its relative narrowness, which is principally due to the 

 lesser development of the antero-internal lobe ; the grooves also are 

 somewhat shallower. The remaining upper teeth ( & - s -) closely resemble 



