EDENTATA OF THE SANTA CRUZ BEDS. 143 



The teeth display a difference from those of Propalceohophphorus, 

 which though slight, appears to be quite constant ; in the last four upper 

 teeth (-&) the division of the postero-external lobe by a vertical groove 

 into two pillars is much more distinct. In both genera there is some 

 variability in this respect and, with sufficiently numerous specimens, com- 

 plete transitions between the two might perhaps be found, but, as a rule, 

 it is not difficult to identify each genus by means of the teeth alone. 



The skull of Cochlops (Plate XXVIII, figs. 1-4) differs hardly at all 

 from that of the preceding genus and yields no diagnostic characters. The 

 difference pointed out by Ameghino ('91, 326; '98, 310) that the fossa 

 for the suborbital process of the zygoma, which in the preceding genus is 

 present on the outer side of the horizontal ramus mandibuli, is lacking 

 in Cochlops, I have not found to be entirely constant. 



What little is known of the skeleton agrees closely with the corre- 

 sponding parts of Propalceohophphorus. 



COCHLOPS MURICATUS Ameghino. 



(Plates XIX, XX, XXIV, Figs. 12, 13 ; XXVIII, Figs, i, 2.) 



Cochlops muricatus Amegh. ; Contrib. al Conoc. de los Mam. Fos. de la 



Repub. Argent, 1889, p. 792. 

 Asterostemma granata Amegh., Ibid., p. 823. 

 Propalceohoplophorus granatus Mercerat ; Rev. del Mus. de La Plata, T. II, 



1891, p. 39. 

 Propalceohoplophorus attstralis Lydekker, in part ; Anales del Mus. de La 



Plata, T. Ill, 1894, p. 45. 



This is the larger species of the genus and its carapace somewhat ex- 

 ceeds in size that of the average individual of Propalceohoplophorus aus- 

 tralis, while the skull is relatively smaller. The carapace and tail-sheath 

 are adequately known only in connection with this species and have 

 already been described in the foregoing account of the genus ; no impor- 

 tant part of the cephalic shield has yet been obtained. The teeth differ 

 from those of the smaller species, C. debilis, in being both actually and 

 relatively broader, and the last upper tooth, A , is considerably reduced in 

 size. 



In the following table of measurements, No. i is from a skull in the 

 Ameghino collection, which is associated with large portions of the cara- 

 pace, but, as the measurements were made from a photograph, they are 



