DESCRIPTION OF FISHES. 201 
in the preceding ; their extremities are also not so pointed: they are very differ- 
ent from those of A. irregularis. 
Aitobates subarcuatus. 
The characters of this specimen agree with Professor Agassiz’s description of 
Ait. subarcuatus ; I have a dental plate of this species 4 inches in width, which 
must have belonged to an enormous fish. It is very difficult to distinguish this 
species from 421. irregularis. 
Mitobates marginalis. (Tab. XII. fig. 1.) 
On showing this specimen to Professor Agassiz, he considered that it was 
distinct from all the former species, and suggested that marginalis would be a 
good name for it. ‘The characters of this species are so obvious and so different 
from any other, that it is at once recognised. The figure (Tab. XII. fig. 1) re- 
presents a portion of the upper jaw; the dental plates are much arched, very 
strong, and ? of an inch in thickness. The margins are apparently bordered by 
accessory teeth, but on the underside the dental furrows extend uninterruptedly 
to the margins—a character which at once distinguishes it from Myliobates. I 
have seen only two specimens ; both are in my own collection. 
AKtobates rectus. (Tab. XI. fig. 8.) 
I have several detached dental plates of different sizes, so straight as to 
justify the above specific name, though in many respects they resemble 4. 
irregularis. 
Tab. XI. fig. 9.—Recent lower jaw of Atobates, showing the natural position 
of the dental plates. From the Museum of the College of Surgeons. 
Tab. XI. fig. 10.—The upper and lower jaws in their natural position from a 
small recent ditobates ; the upper jaw being nearly perpendicular to the lower, 
exemplifying their adaptation for triturating the smaller mollusks and crustacea. 
We find the same curved character of the upper jaw, and adaptation of the dental 
apparatus in the genus Myliobates. 
From the Museum of the College of Surgeons. 
