2762 Bulletin ^7, United States National Museum. 



vomer bluntly conical. Gill membranes broadly united, meeting in an 

 angle, joined to tb(^ istbnius, but with a free margin ; gill rakers 9 + 15. 

 Distance of dorsal from end of snout 2f in the lengtb. Dorsal spine gran- 

 ular on sides and in front, about \ tbe lengtb of the head in height; 

 distance of the adipose fm from tbe dorsal 3^ in the length, the height of 

 tbe adipose lin about 'l\ in its length, which is contained 2* in the length 

 of tbe head. Caudal deeply forked, 5^ in the lengtb; anterior 3^ of the 

 anal strongly convex, the jiosterior \ slightly emarginate, tbe highest ray 

 about 2\ in bead. Ventrals reaching to anal, about 2 in head, their dis- 

 tance behind the dorsal equal to tbe lengtb of dorsal and \ the dorsal 

 plate; pectoral spine granulose on sides, the outer margin with a series 

 of larger granules which become recurved notches toward the tip, the 

 inner edge with recurved hooks, its height If in the length of the head; 

 a small pectoral pore; no evident series of vertical pores. Bluish gray 

 al)ove, becoming white beloAv; the fins brownish with dots. Descrip- 

 tion from the type oi Ar'ius alaius, .68 m. long, from Panama; collected by 

 Dr. Steindachner. (Eigenmann & Eigenmann, Nematognathi, 61.) 



Selenttspis dowii is thus characterized by Jordan & Gilbert:* Head 4 

 m with caudal) ; depth 6^ (7*) ; width of head 5,1 . D. I, 8 ; A. 4, 12. Length 

 (29529, U. S. Nat. Mus.) 10 inches. Body elongate, narrow, and slender, 

 the caudal peduncle 1| in head. Head low and narrow, tapering ante- 

 riorly, the snout subtruncate. Eye small, 7 in head, placed rather high; 

 interorbital space little arched, with ridges and depressions, 2* in head; 

 snout 3* in head; breadth of mouth 2^ in head. Mouth moderate, with 

 thinnish lips; teeth villiform, bluntish; vomerine teeth forming 2 small- 

 ish, rounded patches, separated l)v a moderate interspace; each patch 

 confluent with the neighboring palatine patch, which is rounded and 

 rather large; tbe suture marked by a constriction; palatine bands with- 

 out ]>ackward prolongation; premasillary baud of teeth broad. Barbels 

 very long; maxillary barbel extending well beyond tip of pectoral fin; 

 outer mental barbel reaching well past front of pectoral; inner 2* in head. 

 Dorsal shield comparatively large, not distinctly crescent-shaped, its 

 divisions produced backward, their length about twice tbe length of the 

 shield on the median line; anterior margin with 2 emarginations, the 

 point fitting into an emargination of the occipital process; dorsal shield 

 without keel. Occipital process very broad and short, its edges nearly 

 straight, its breadth at base considerably greater than its length; its 

 median line with a rather low keel. Fontanel broad and very short, 

 ending obtusely at a point not far behind eye, tlie distance from this 

 point to tip of snout If in its distance from base of dorsal; each side ol' 

 fontanel with a conspicuous smooth ridge, the 2 ridges converging 

 anteriorly; shields of head rather finelj' granulated, few of tbe granula- 

 tions forming lines, none of them extending farther forward than posterior 

 margin of eye. Opercle striate. Gill membranes meeting below in a sharp 

 angle, fornung a rather broad fold across isthmus. Dorsal spine very 

 short, its length a trifle less than pectoral spine, 2^ in head. Axillary 

 pore obsolete. Humeral process granulated, rather narrowly triangular, a 



*Bull. U. S. Fish Comm., n, 1882, 50. 



