FISH. 131 
agrees with the SiJuride in having no cecal appendages, though the air-bladder 
is similar to that of the ordinary Salmonide. There are some peculiarities con- 
nected with the anal and sexual orifices which I shall notice presently, along with 
other points in the internal structure, in the species to be described first. 
Mr. Darwin has brought home two species of this new genus, agreeing precisely 
in form, but very distinct in respect to size and colouring. 
1. ApLocurron Zepra. Jen. 
Puate XXIV. Fie. 1. 
A. obscure plumbeus ; fasciis nigris transversis: maxillis equalibus. 
Base De ht] Av Oia CMGy &er- Pts War 
Lone. unc. 9. lin. 6. 
Form.—General form somewhat resembling that of the Mackarel, elongated, and approaching to 
fusiform. Greatest depth about the middle, equalling one-sixth of the entire length. Line of 
the back and profile nearly straight, the latter falling very little. Greatest thickness rather 
more than half the depth. Head small, contained about five and a half times in the entire 
length. Snout short, but rather acute. Mouth with a moderate gape reaching to beneath the 
anterior angle of the eye: when shut, both jaws equal, the lower one ascending at an angle of 
45° to meet the upper; when open, the lower one a little the longest. Margin of the upper 
jaw formed by the intermaxillary, the maxillary appearing behind it. A single row of small 
but sharp teeth extending along the entire margins of both jaws: a double row of similar teeth, 
but stronger and more curved, down the middle of the tongue; also a double row along 
the middle of the vomer. Eyes moderate; their diameter four and a half times in the length 
of the head; distant about one diameter and a quarter from the end of the snout, 
and with an interval between them of about one and a half. Nostrils with two orifices, both 
roundish, one before the other, with a little interval between, the posterior one rather the 
largest. ‘Two distinct pores on each side of the crown, one behind the other with an interval 
between, above and rather behind the eyes. Gill-opening very large, the membrane with only 
three flattened rays, deeply notched beneath, the notch reaching to beneath the middle of the 
eyes. All the pieces of the opercle present, but the interopercle only just appearing behind 
the angle of the preopercle, and the subopercle forming but a narrow lanceolate lamina beneath 
the true opercle, which last constitutes the greater portion of the gill-flap, and is of an oblong 
form, the posterior margin being cut straight and vertical. 
The whole skin perfectly naked everywhere, without the least vestige of scales. No lateral 
line, except a faint streak, passing along the middle of the sides, be so called. Dorsal com- 
mencing at the middle of the length, this last being measured to the base of the caudal fork ; 
of the same form as in the ordinary species of the genus Salmo; its greatest height a little 
exceeding its length, which last is rather more than half the depth of the body; first ray simple, 
the rest branched. Adipose small, and just half way between the end of the dorsal and the 
base of the caudal. Anal of a somewhat triangular form, the margin sloping very much off 
backwards, commencing a little beyond the tip of the reclined dorsal, and terminating opposite 
