EDENTATA OF THE SANTA CRUZ BEDS. 157 



been found indicate that this structure was probably quite different from 

 the head-shield of the other genera : the plates are separate and display 

 hardly any remnant of an ornamental pattern, but have a punctate surface, 

 some finely and others coarsely granular ; the large postero-median plates 

 resemble those of Cochlops in having two concentric rings of conspicuous 

 pits, but the surface is more rugose. 



The teeth are, in general, like those of Propalceohoplophorus, except 

 that in the posterior region of the upper jaw (^~ & ) they have the postero- 

 external lobe much more deeply divided, making four outer lobes. 



The special peculiarity of the genus is in the form of the rostrum, which 

 is very short, with its dorsal surface sloping very steeply downward, sug- 

 gestively like the rostrum of Panochthus. This character is particularly 

 well shown in the type-species, M. ttevatus, while in the presumably older 

 M. anceps it has not been carried so far. 



It is not at all improbable that in this genus we have the ancestor of 

 Panochthus, but this conclusion must remain merely tentative until much 

 more complete material has been obtained. 



METOPOTOXUS L^EVATUS Ameghino. 



Asterostemma Icevata Amegh.; Contrib. al Conoc. de les Mam. Fos. de 



la Repub. Argent, 1889, p. 823. 

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



II, 1891, p. 38. 

 Propalceohoploplwrus australis Lydekker, in part ; Anales del Mus. de La 



Plata, T. Ill, 1894, p. 48. 



Aside from plates of the carapace and head-shield, the only known 

 examples of this species are two fragments of skulls in the Ameghino 

 collection, each containing most of the upper teeth of the right side. The 

 anterior teeth, - and -, are relatively larger than in the preceding genera ; 

 - has a very small median external pillar, while in the preceding genera 

 this tooth has a broad median valley on the outer side ; it also has a sub- 

 divided postero-external lobe. This division of the postero-external lobe 

 is repeated on all the succeeding teeth ( i ~ A ) to a degree even more 

 marked than in Cochhps. The rostrum is extremely short and the fore- 

 head strongly convex, with upper contour sloping downward very steeply. 

 The lachrymal foramen has a very elevated position. 



