EIGENMANN : THE FRESHWATER FISHES OF BRITISH GUIANA 237 



Ancistrus Kner. 

 Ancistrus Kner, Denkschr. Akad. Wiss. Wien, VII, 1853, 272 (sp.). — Bleeker, 



Nederl. Tijdschr. Dicrk., I, 1863, 77 (cirrhosus). 

 Thysanocara Regan, Ann. and Mag. Nat. Hist., (7), XVII, 1906, 95 (cirrhosus). 



Type, Ancistrus cirrhosus Kner. 



I have elsewhere {Science, n. s., XXI, 1905, 794) given my reasons for the 

 use of the name Ancistrus for this genus. 



Premaxillaries and dentaries of nearly equal length; interopercle movable; 

 snout naked, with tentacles. About eleven species. 



Key to the Guiana Species of Ancistrus. 25 

 a. Fins, especially the dorsal, with conspicuous cross-bands over rays and membranes; body with large 

 whitish spots, the dark background reduced to vermiculations; ramus of the lower jaw 2.3-3 



in the interorbital temmincki. 



aa. Fins, especially the dorsal, with faint dark spots along the rays; mandibular ramus 2-3 in inter- 

 orbital; interorbital 2.4 in the head; depth about equal to interorbital; naked portion of snout 

 of the male reaching nearly half-way to posterior margin of the eye, with a Y-shaped series of 



tentacles; obscure, medium-sized light spots, especially on the ventral surface cirrhosus. 



aaa. Fins, especially the dorsal, plain, or frequently with minute white dots, the dorsal and caudal often 



margined with lighter. 



6. Mandibular ramus 2.75-3.75 in the interorbital; interorbital 2.25 in the head; dorsal and upper 



angle of caudal narrowly margined with light, or not margined; naked part of snout in the 



male with about four tentacles in a straight line; naked part extending one-fourth the distance 



to posterior margin of eye along median line. Minute white dots on fins and body. 



hoplogenys. 

 66. Mandibular ramus 2.0-2.4 in the interorbital; dorsal and caudal conspicuously margined with 

 white or yellow. Naked portion of snout, in adult male, reaching half-way to posterior 

 margin of eye, in the female one-third the distance to posterior margin of eye. Inter- 

 orbital 2.S-3 in head; depth 6.8 in the length. Tentacles in male in a Y-shaped figure. 

 Occipital finely granular, the granules scarcely arranged in radiating lines; base of dorsal 

 equal to the distance from base of last ray to tip of spine; caudal very oblique, the upper 

 lobe about 14 the length of the lower; minute white dots on fins and body, otherwise 

 plain black lithurgicus. 



104. Ancistrus temmincki iCuvierand Valenciennes). 

 Hypostomiis temminckii < 'uvier and Valenciennes, Hist. Nat. Poiss., XV, 1840, 



514 (Cayenne). — Muller and Troschel, in Schomburgk, Reisen, III, 1848, 



631 (Takutu). 

 Ancistrus temtninckii Bleeker, " Silures de Suriname," 1864, 11, pi. 1, fig. 3, pi. 2, 



fig. 2 (Surinam). — Eigenmann and Eigenmann, Proc. U. S. Nat. Mus., XIV, 



25 Regan gives Ancistrus dolichoptera Kner as found in Guiana. Xo definite locality is given. 

 If it should be found within the region covered by the present paper it can readily be distinguished by 

 its having D. 1,8 or 9. 



