18 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
A second specimen is only three inches and a quarter in length; but differs 
in no respect from the above, except in having one soft ray less in the anal fin. 
Habitat, River Matavai, Tahiti. 
Several of the species in this genus are extremely similar as well in form as 
in colours. Possibly that which I have here characterized as new may not be 
distinct from the D. malo of Valenciennes, which comes from the same country ; 
but the description in the ‘“ Histoire des Poissons” is so brief, that it is hardly 
possible to determine this point with certainty. It has, however, two, and one 
specimen three, soft rays less in the anal fin. It is also closely allied to the 
D. marginatus, from which it hardly differs, excepting in having the denticula- 
tions of the preopercle rather stronger, and the tenth dorsal spine shorter in re- 
lation to the soft rays which follow. The D. marginatus, however, comes from 
Java. The species here described was found by Mr. Darwin in Tahiti, in the 
river of Matavai. 
HELOTES OCTOLINEATUS. Jen. 
Hf. corpore lineis longitudinalibus nigricantibus octo; pinnis dorsali, anali, caudali- 
gue, maculis fuscis; verlice striis elevatis duobus subparallelis; preoperculo distincte 
denticulato, et ad marginem limbi internum subcristato ; operculo mucronibus duo- 
bus, superiore minimo; squamis ubique levissimis. 
B62 Di 12/9 Ara Ctr, weer wlos Vio: 
Lone. unc. 9. Jin. 9. 
Form.—Body oblong. Greatest depth exactly four and a half times in the entire length. Length 
of the head rather less than the depth of the body. Snout short and obtuse. Jaws exactly 
equal: each with a broadish band of velutine teeth, which are all, apparently even the most 
minute, three-pointed, although this character is not very obvious except in the outer row, which 
are longer than the others. No vomerine teeth appear externally, but they may be felt through 
the skin of the palate, and on dissecting this off, there is brought to view a small hard disk 
rough with minute asperities. Mouth very little cleft, the commissure not extending more 
than half way between the end of the snout and the anterior margin of the orbit. Eyes rather 
large ; their diameter one-fourth the length of the head. Maxillary, when the mouth is closed, 
concealed in part beneath the suborbital, the lower margin of which is somewhat sinuous and 
obscurely denticulated, the denticulations being concealed by the membrane and more easily 
felt than seen. The denticulations on the preopercle very manifest. The principal spine on 
the opercle slender and very sharp, not exactly straight, but slightly curved, the convexity of 
the bend being downwards; above is a second spine, but very small and easily overlooked. 
