108 



U. S. p. R. E. EXP. AND SURVEYS — ZOOLOGY — GENERAL REPORT. 



the total length, in which the caudal fin itself enters ahout five times and a half The gape of 

 the mouth is oblique upwards, the lower jaw being the longest, and the posterior extremity of 

 the maxillary, which is quite dilated, extending to a vertical line drawn in advance of the orbit. 



The origin of the anterior dorsal fin takps place posteriorly to the insertion of the ventrals, 

 and is somewhat higher than the second. The origin of the anal is situated a little posterior to 

 that of the second dorsal, and terminates almost evenly with the latter. The terminal ray of 

 both of these fins, though united to them, resembles more an isolated finlet than an ordinary 

 ray. It is larger than those preceding it, and hence quite conspicuous ; its tip reaches the 

 rudimentary rays of the caudal above as well as below. The caudal fin is deeply furcated. 

 Br. VII : VII ; D VIII, 40 ;? A II, 1, 28 ; C 6, 1 , 9, 8, 1, 6 ; V i, 5 ; PI, 22. 



The scales of the body are not preserved upon our specimens ; a few scattered ones exhibit a 

 pectinated or rather spiny posterior edge, numerous and fine concentric striae, but no radiating 

 furrows. The lateral line, from the upper edge of the opercle, extends nearly parallel with the 

 back to the beginning of the second dorsal, where a gracefully ojien curve brings it along the 

 middle of the tail, hence runs straightway to the caudal. The scale-like scutellae of which it is 

 composed are vertically elongated and quite narrow, largest upon the middle of the tail and 

 smallest upon the bent, excei)t near the base of the caudal, where they taper off into exiguous 

 plates. Their middle region is keeled, inconspicuously anteriorly, prominently along the tail, 

 the keel increasing towards the caudal fin. 



The specimen before us being somewhat discolored, we have nothing to add touching its 

 various tints, having quoted in the specific diagnosis the coloration as observed by Dr. Ayres 

 on a fresher specimen. 



List of specimens. 



2. TKACHUKUS BOOPS, Grd. 



Spec. Char. — Head contained a liUlc over four limes and a half in the total length. Posterior e.xtremity of maxillary 

 extending to a verlical lino intersecting the anterior rim of the pupil. Curve of lateral line situated in advance of the second 

 dorsal fin. pectoral fins very long, slender, and falcate. Greyish olivo above; yellowish beneath. A black patch at the 

 posterior edge of the opercle. Fins uniculor. 



As the specimen upon which this species is established may be considered of mature growth, 

 its characters will better compare with those of tlie preceding one, and especially with the 

 description of the latter by Dr. Ayres. 



Its total length measures twelve inches, the head being contained in it a little over four times 

 and a half, and exactly four times to the fork of the caudal fin. The body is elongated, very 

 much compressed, subfusiform in its profile, and of great symmetrical beauty. The greatest 

 depth which corresponds to the origin of the second dorsal enters about four times in the total 

 length. The upper surface of the head is sub-convex, and gently declivous forwards, the snout 

 being rounded and rather obtu.se, the lower jaw jjrojecting slightly beyond the upper, owing to 

 the obliquity upwards of the gape of the mouth. The maxillar bone ia quite dilated posteriorly 



