240 SILURID-E. 



95. CHJETOSTOMUS*. 



Chsetostomus, Heckel\, in Tscltndi, Faun. Per. Pisces, p. 25. 



Hypostomus, sp., Cuv. ^ Vol. xv. p. 50.3. 



Chsetostomus et Ajicistri brachypteri, Ener, Denkschr. Acad. Wiss. 



1854, vii. p. 256. 

 Ancistrus, Hpiniancistrus, Chsetostomus, Paraucistrus, et Pseudacan- 



thicus, Bleek. Nederl. Tydschr. Dierk. 1863, p. 78. 



This genus differs from Hjipostomus in having the interoperculiim 

 very moveable and armed with erectile spines ; the number of dorsal 

 rays varies betAveen eight and ten. 



Continent of tropical America ; Porto Rico. 



Some ichthyologists are of opinion that the species of this genus 

 are subject to changes in the development of the pectoral spines, of 

 the dorsal rays, and of the armatiu'e of the interoperculiim, and, 

 further, that the sexes differ in external characters. If this be so, 

 it is certainly not the case in all the species, as I have found young 

 and old individuals, of ojie and the same species remarkably alike, 

 if obtained at the same locality. However, the eye and the head 

 always appear to be larger in young individuals than in old ones, 

 as has been already lu-ged by Kner on different occasions. The 

 species themselves are imperfectly known, as they are not largely 

 represented in collections made in South America. Most of them 

 appear to be local, and therefore we may expect numerous additions 

 to the already considerable number of species known. There are 

 many intermediate forms between the species -with elevated and 

 mailed head, and those with depressed head and soft-sldnned snout, 

 so that but little value can be attached to the subgeneric di\'isions 

 which have lately been proposed. 



The species may be divided as follows : — 



I. Margin of the snout with hard granidations. 



a. Dorsal fin nine-rayed: Pseiidacantliicus, Blkr., p. 241. 



0. Dorsal fin eight-rayed. 



* Scutes of the body with distinct keels ; dorsal fins distant : He- 

 miancistrns, Blkr., p. 242. 



** Scutes of the body without distinct keels; dorsal fins distant: 

 Ancistrus, sp., Blkr., p. 244. 



*** Dorsal fins subcontiniious : Parancistrus, Blki\, p. 240. 



* 1. Hypostomus bufonius, Cuv. ^ Vol. xv. p. 611. — Rio ApurLmac (Peru). 



2. temminckii, Cuv. ^ Val. xv. p. 514. — Cayenne. 



3. Hypostoma squaHnum, Schonib. Fish. Brit. Giiian. i. p. 142. pi. 2. — British 



Guiana, 

 t Although Tsehudi claims the authorship of tliis genus and of the tyjDical 

 species {Ch. loborhynchus), it is evident, from the scientific character of the de- 

 scription, that it is from another pen. Kner, indeed, informs us that it is Heckel 

 who named, described, and figured that genus and the species in the 'Fauna 

 Peruana.' This fact reminds us of a similar claim laid by Bibron to some of 

 the genera of Batrachians published by the same author. 



