FISHES. 49 
There is no dorsal fin. The caudal fin surrounds the extremity of the tail, extending a little 
farther forwards above than below, and tapering gradually towards, or else rising grad- 
ually from, the outlines of the caudal region. The anal fin is long, but very low. The vent 
is situated about six tenths of an inch from the posterior margin of the latter fin. 
The precarious state of keeping the unique specimen which was obtained at Valparaiso, 
leaves us in doubt as to whether the bluish slate color of its epidermis was a true approxima- 
tion towards its natural hue. 
Plate XX XIII, fig. 1, represents Bdellostoma polytrema, size of life. 
fig. 2, is an outline of the head, seen from above, exhibiting the cephalic 
distance between the eyes, the position and direction of three pairs of ten- 
tacles. 
fig. 3, being a front view of the head, exhibits the nasal opening (a), and 
the same tentacles as in fig. 2. 
fig. 4, which is the head, seen from below, shows the four pairs of tentacles, 
(b, c, e,f,) as well as the mouth (d), and nasal aperture (@). 
fig. 5, is the tongue, with its double and arched series of conical teeth—a 
being two detached teeth, and } the palatine tooth. 
