ISISTIUS. 33 
the tail. Its body is rather long and rounded, its head is small and taper- 
ing; it has moderately large spiracles and narrow gill openings; and its 
teeth differ greatly in shape and mobility on the two jaws. Its fins, except- 
ing the caudal, are all small; the dorsals differ little in size or shape and 
both are behind the middle of the body. The eyes are large, the nostrils 
are small and the body is phosphorescent. The single known genus is 
probably nocturnal and descends to great depths, though not an inhabitant 
of the bottom. 
IsISTIUsS. 
Scymnus, Quoy and Gaimard, 1824, part. 
Leius Kner, 1865, Denkschr. Ak. Wien, XXIV., Extr. p. 9 (Nov. 10, 1864), characterized. 
Isistius Gill, 1865, Pr, Phil. Ac., 264 (Nov. 22, 1864), named. 
Body elongate, subcylindrical, tapering backward, abdominal cavity long. 
Head moderate in size, narrowing forward, depressed. Snout subconical, 
blunt. Nostrils anterior. Mouth inferior, transverse, with a deep groove 
in front of the upper jaw and a deep fold behind each angle. Lips well 
developed; lower labial fold at the angle of the mouth, short, rounded, 
valvular. Teeth in the upper jaw small, raptorial, erectile, lanceolate, those 
of several series in function at once. Teeth of the lower jaw large, sectorial, 
erect, fixed, blade-like, the single series in function forming a continuous 
serrate-edged plate. Eye large, lateral; orbit cireular in front, angled 
behind; no nictitating membrane. Spiracles medium, on the top of the 
neck. Five small gill openings, not in a groove. No anal fin. Dorsals 
small, without a spine, similar, anterior backward of the middle of the body. 
Caudal short and deep. A short dermal fold on the side of the tail. Lat- 
eral system tubular. Stomach very long; intestine short, with a spiral 
valve. Scales small, depressed, in pavement. 
So far as yet determined the range of the known species extends through- 
out tropical seas to fifty-five degrees from the equator. 
The generic name is given as accepted by others, though the records 
appear to favor the name Leius given by Kner. 
