488 THE AMERICAN NATURALIST. 
but two large-sized fragments in the Schultze Collection fur- 
nish sufficient evidence of a distinct species. They indicate a 
jaw of about twice the size of R. rostratus, and are heavier in 
proportion. Concentric striz are more prominent than in the 
last-named species, and one of the specimens shows minute 
folds crossing the striz at right angles. These have the 
appearance of fine cracks on the gently rounded anterior 
margin where they have been somewhat corroded. The sym- 
physis is constituted similarly to that of the preceding species. 
The eighteen or more examples of R. rostratus in the collection 
are too nearly of a size to be regarded as all young forms, of 
which P. major is the adult, and it would be strange indeed 
if full-grown individuals were. outnumbered ten to one by 
more readily destructible immature examples. Close resem- 
blances exist, however, between the anterior regions of R. ro- 
stratus, the present species, and Paleomylus predator (Fig. 43). 
(To be continued.) 
