128 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



length, the lobes equal. Ventrals more forward than in the other species, decidedly in advance 

 of the dorsal, and attached at one-third of the entire length ; their axillary scale very small. 

 Pectorals narrow, reaching beyond them. No long folds of skin accompanying the rays of the 

 vertical fins. 

 Colour.— Not noticed in the recent state, in which, judging from its appearance in spirit, it was 

 probably silvery, or perhaps golden, with somewhat of an olivaceous hue becoming deeper on 

 the back. There are evident remains of a bright longitudinal lateral band : also of a black spot 

 at the base of the caudal. The dorsal and the anterior portion of the anal incline to dusky : 

 the pectorals and ventrals are slightly dusky at their extremities ; there is also a large irregular 

 dusky stain on the back and shoulders anterior to the dorsal fin. 



A second specimen differs from the above in being a trifle smaller, and not quite so deep in 

 the body. The anal is also decidedly scabrous, as in the T. scabripinnis, and has one ray less in 

 it. The colours are similar, excepting that the fins are rather less dusky, and the large dusky 

 stain on the back and shoulders is wanting, 

 Habitat, Maldonado. 



This species is one of several that were taken by Mr. Darwin at Maldonado, 

 in the lake that had been suddenly drained, before alluded to. It is immediately 

 distinguished from all the others in this genus above described, by its small mouth 

 and abbreviated lateral line. The circumstance of the anal fin being scabrous in 

 only one of the specimens leads to the suspicion that this may be a sexual charac- 

 ter, perhaps common to this and several species ; and, judging from its somewhat 

 less depth, I conceive the specimen so distinguished in this instance to be a male. 



Hydrocyon hepsetus. Cuv. 



Hydrocyon hepsetus, Cuv. Reg. An. (ed. 2) torn. ii. p. 312. 

 falcatus, Freycinet, (Voyage) Zoologie, p. 221, pi. 48. fig. 2. 



f orm.— -Back rising slightly from the nape, whence the profile in front falls obliquely in nearly a 

 straight line to the mouth. Depth contained about three and a half times in the length, caudal 

 excluded. Both head and body much compressed, the greatest thickness being only two-fifths 

 of the depth. The length of the head equals the depth of the body. Snout appears rather 

 pointed when the jaws are shut ; when open, the lower jaw is a little the longest. Gape con- 

 siderable. Maxillary long, commencing before the eyes, and reaching to a vertical from the 

 posterior part of the orbit ; inclining downwards, lapping obliquely in part over the lower jaw, 

 gradually widening towards the posterior extremity, which is rather obliquely rounded. Inter- 

 maxillary with two sharp canines in front, then on each side four or five very small hooked 

 teeth, then another large canine, though not so large as those in front ; behind this commences 

 the maxillary, which is armed all along its margin with a regular row of small equal hooked 

 teeth, resembling sharp serratures ; a similar row on each palatine, but none on the vomer or 

 tongue ; this last pointed, and free at the tip. Lower jaw with two strong canines in front, 

 larger than those in the upper, and fitting into two holes above, when the mouth is shut ; on 

 each side of these are three only half their size, but increasing backwards, placed at rather wide 



