2080 Didlctin //, United States National Mnsetun. 



2423. XEXOCHIRUS PENTACAXTHUS,* Gilbert. 



B. 6 ; 1 D. 5 to 7 ; 2 D. 5 to7 ; A. 6 to 8 ; P. 14 or 15 ; V. 3 (1, 2) ; C. 1-12-1 ; ver- 

 tt'brii? 12 + 28 = (40). Pyloric cceca 5 (1 individual). Body 8-hedra], 

 slightly depressed; peduncle considerably depressed, hexagonal, the lat- 

 eral faces narrow. Spines of body small and sharji, projecting backward 

 nearly parallel with axis of body, decreasing gradually in size from head 

 to caudal in the dorsolateral and superior lateral series, poorly developed 

 on the inferior lateral series only from behind the pectoral to opposite 

 front of anal, entirely absent from the ventrolateral series. Plates on 

 breast, 2 pairs in front of ventrals, followed anteriorly by 3 median single 

 plates; on each side of these'a longitudinal row of 4 or 5 smaller plates, 

 continuous with the ventrolateral series; outside of these the plates form- 

 ing the edge of the breast. Branchiostegal memliraue posteriorly with 3 

 or more very weak plates medially, or none at all ; none on the mem- 

 branes laterally ; 2 or 3 fairly developed ones in front jiart of under side 

 of lower jaw; the membrane behind vent studded with several poorly 

 developed plates, none between ventrals and vent. Head as in X. latifrons, 

 l)ut more depressed and slender; snout not quite so short, blunt; greatest 

 depth of head f of its width, the latter 7 in length of body; orbits large, 

 oval, their longitudinal diameter 21 in head; a slightly curved row of 4 

 or 5 backwardly directed small spines on eyeball just above pupil; inter- 

 orbital space deeply concave, with minor ridges Aery narrow, about 3^ in 

 long diameter of eye, 9 in head ; a single pair of sui>raocular spines ; the 

 poorly developed occipital ridges with 2 pairs of spines, of which the 

 anterior is very low and blunt; temporal ridges moderate, terminating in 

 a blunt spine ; the interrupted ridge across cheek less prominent and shelf- 

 like than in A', latifrons, bearing 1 spine (sometimes 2) in front of anterior 

 inferior angle of orbit, 1 or 2 on suborbital, and a single broad flat spine 

 (sometimes preceded by a very small one) at posterior edge of preopercle; 

 cheek below ridge entering into ventral surface of head with a longitudinal 

 seriesof 3or 4 plates; nasal spines sharp, far apart; median rostral plate 

 small, movable, variable, its lateral expansions exposed as spines and with 

 3 (in 1 specimen 4) diverging spines directed upward and backward; not 

 projecting beyond premaxillaries; maxillary reaching very little beyond 

 front of orbit, entirely covered by preorbital. Jaws equal; teeth on jaws, 

 vomer, and palatines. Two barbels at tip of each maxillary; those on 

 under side of mandible inconstant; occasionally a very small pair near tip 

 of jaw, at the 2 ends of the terminal mucous pore; another at edge of next 

 mucoiTS pore nearly constant, but very variable, long, short, or only a small 

 pimple, single, double, or even a pair on each side; occasionally a very 

 small one at edge of third pore. Dorsal fins separated by a moderate 



* Diagnosis : Body slightly depressed, its depth a little less than its width, tapering 

 moderately, and the tail tapering more gradually toward the caudal ; width of body at 

 base of pectorals 7 in length ; liead4J; plates in dorsal series 39; from occiput to first (lor- 

 sal 7 or 8, between dorsals 5 or 6, fi'om ventrals to anal 12 or Ki pairs; barbels 2 at tip of 

 maxillary, those on lower jaw inconstant, usually 2 pairs. Median rostral plate small, 

 nearly vertical, with 3 upright spines; nasal spines prominent, separated; 1 pair of supra- 

 ocular and 1 pair of occipital spines. Teeth on jaws, vomer, and palatines ; gill membranes 

 joined to isthmus without free fold. Brownish olive above, pale below ; 4 or 5 dusky cross 

 bars on back. 



