1712 BtiUetin ^7, United States National Musewn. 



f height of first; no trace of a third spine, the membrane extending 

 almost to posterior end of groove, the length of its base about \ snout; 

 second dorsal and anal not falcate, the upper outline straight, the fins 

 becoming uniformly lower posteriorly ; caudal fin slightly convex behind, 

 the tips produced for a distance about equal to diameter of orbit ; plates 

 very rough, with broken ridges radiating from base, essentially similar 

 in shape on sides of body and head, showing no tendency to coalesce 

 on cheeks; 8 raised lines formed of rough median crests on the plates 

 on posterior part of sides, the crests not bearing distinct spines; several 

 enlarged plates immediately behind the opercle, each with centrally 

 radiating lines; pelvic spine very rough, as well as the membrane imme- 

 diately behind it. Color, very deep cobalt blue in life, becoming uni- 

 formly black in spirits; a narrow light blue line along bases of dorsal and 

 anal, becoming white in spirits ; caudal with an intramarginal black band, 

 edged posteriorly with a very narrow white line. Very abundant at 

 Clarion and Socorro islands. {Mspinosus, having 2 spines.) 



MelicMhys bispinosus, Gilbert, Proc. TJ. S. Nat. Mua. 1890, 125, Clarion and Socorro 

 islands, of the Revillagigedo Archipelago. (Coll. Albatross.) 



Family CLXX. MONACANTHID^. 

 (The Filk Fishes.) 



Body much compressed, covered with very small rough scales, forming 

 a velvety covering; males sometimes with spines on the caudal peduncle. 

 Upper jaw with a double series of incisor- like teeth, 6 in the outer, and 

 4 in the inner series; lower jaw with 6 similar teeth in a single series; 

 first dorsal with a single strong spine and generally a rudimentary one 

 behind it; second dorsal long, similar to anal; ventral tins reduced to a 

 simple osseous, fixed or movable, small appendage at the end of the long 

 pelvic bone; this appendage often rudimentary or entirely absent; no 

 barbel; vertebne 7-|-ll to 14=18 to 21. Genera 6 or more; species about 

 50. Herbivorous shore fishes of warm seas, closely allied to the Balistidw, 

 differing chiefiy in having the first dorsal represented by a single spine, 

 behind which is sometimes a rudiment; scales small, spinigerous, the skin 

 mostly rough velvety. The species are mostly small in size and are not 

 used as food, having little flesh and that of a bitterish taste. (Genus Mo7i- 

 aeanthus Giinther, Cat., viii, 229-254, 1870). 



a. Pubic bone with a small spine at its end ; gill opening sbort, nearly vertical ; dorsal 

 and anal moderate, each of leas than 40 rays. 

 b. Pelvic spine movable. 



c. Dorsal spine not barbed, its edge merely rough. Cantheeines, 672. 



cc. Dorsal spine armed with .strong retrorse barbs, usually in 2 series. 



MONACANTHUS, 673. 



bb. Pelvic spine fixed; dorsal spine with about 4 series of small barbs. 



PSEUDOMONACANTHUS, 674. 



aa. Pubic bone without spine at its end, gill opening long, oblique; dorsal and anal 

 long, each of 40 or more rays ; dorsal spine without barbs, inserted above the 

 orbit. Alutera, 675. 



