4112 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
in the form of a narrow fissure nearly to the base of the interparietal process, but is not very 
obvious, except between the eyes, where it opens into a sort of elongated ellipse. There are 
eight or nine pores on the top of the head, rather behind the eyes, so arranged as to form 
nearly a complete circle. There is also a very conspicuous row of three or four large oval 
pores on the cheek, at the anterior part of the opercle, descending obliquely forwards: other 
smaller ones may be seen scattered about different parts of the head. The jaws are equal: 
the teeth as in the last species, excepting that a roughness can be distinctly felt upon the 
vomer beneath the skin, though there are no teeth on that part which appear through it. The 
maxillary pair of barbules reach to a point midway between the insertion of the ventrals and 
the commencement of the anal: of the submandibular pairs, the exterior do not reach beyond 
the insertion of the pectorals; the interior are two-thirds the length of these. Eyes elliptical, 
the longitudinal diameter about one-fifth the length of the head; situate nearer the end of 
the snout than the posterior part of the opercle; the interval between them nearly two 
diameters. ‘The lateral line slopes downward till opposite the fourth soft ray of the dorsal, 
then passes off straight along the middle to the caudal. 
The pectorals are contained about five-and-a-half times in the entire length. The spine 
is similar to that of the last species; but the humeral bone is shorter, and scarcely one-third 
of the pectoral itself. The dorsal is similar; and the space between it and the adipose is the 
same; but the adipose itself, though of the same form, is not so long, from the body being less 
elongated; it is not more than half as long again as the dorsal. Anal similar, but the adipose 
not advancing so much beyond it. Caudal and ventrals similar; but the former with the 
lobes equal. 
Cotour.—(In spirits.) On the whole similar to, but darker than that of the last species. There 
is some appearance of a fascia along the lateral line. The upper part of the dorsal, and also of 
the anal, is dusky, but there is no spot on the adipose. Pectorals and yentrals dusky. 
A second specimen differs from the above in no respect, except in being smaller, measuring 
two inches and a quarter in length, and in having one ray more in the anal. 
Habitat, Rio de Janeiro? 
The number annexed to this species has been lost, but there is reason for 
believing that Mr. Darwin took it with the last at Rio de Janeiro. I cannot iden- 
tify it with any of those described by Cuvier and Valenciennes in the “ Histoire 
des Poissons.”—It affords another instance of the indefiniteness of the character 
derived from the presence or absence of vomerine teeth; since a band of such 
teeth, which are considered by Valenciennes as absent in this genus, can be 
distinctly felt and made obvious by removing the skin of the palate, though they 
do not appear externally. This is not the case with the species last described, to 
which nevertheless, the present one approaches so closely in general character, 
that they never could be widely separated. Except for the greater elongation of 
the body in the P. gracilis, I should have been almost inclined to consider them 
as sexes of the same species. 
