1894.] 9* [Cope, 



HisONOTUs NiGRiCAUDA Boulenger. Otocindus nigricauda, BouL, Pro- 

 ceeds. Zool. Soc, London, 1801, p. 234 ; PL xxv, Fig. 3. 



One si^ecimen. This species differs from those described above, in the 

 presence of only two nuchal scuta between the occipital bone and the 

 base of the first dorsal ray, as represented in Boulenger's figure. In this 

 point it agrees with the two species of Otocinclus to be described below. 

 In the two species of Hisonotus referred to, there are four nuchal plates 

 crossing the same space. 



The specimen of H. nigricauda measures, only 30 mm. The sides and 

 posterior two thirds of the middle line of the belly are squamous, the 

 remainder smooth. 



Otocinclus flexilis sp. nov. 



Head large, muzzle rather short, width posteriorly equal depth of body 

 at first dorsal spine, and entering the length less the caudal fin four and a 

 quarter times. Eye entering length of head four times, and interorbital 

 width three times. Body compressed ; superior and inferior aspects 

 of caudal peduncle flattened, and separated from sides by an angular 

 keel. Surtuces ever^'where hispid. Perforations of supratemporal plate 

 numerous. Lower lip very thin, and entirely smooth. Plates of belly in 

 two lateral rows which are directed forwards, and are separated by a 

 single row on the middle line, which is sometimes more or less incom- 

 plete, thus permitting those of the lateral series to come in contact. 

 Occipital plate angulate posteriorly, and separated from dorsal spine 

 by two transerse plates and a small median posteriorly. 



The pectoral spines reach the base of the ventral fins, and the ventrals 

 fall considerably short of the anal. Caudal lobes acute, subequal. Radii, 

 D. I. 7 ; P. I. 6 ; V. I. 5 ; A. I. 5. The spines are all strongly hispid, 

 and those of the pectoral fin are more robust than that of the dorsal. 

 Plates ol lateral line, 25. 



Light yellowish brown, with a row of about' six oblong dusky spots 

 along the lateral line, which become obscure anteriorly. A series of 

 corresponding spots along the dorsal region. Dorsal and caudal fins light 

 colored with numerous dusky spots. A black spot at the base of the cau- 

 dal fin in some specimens. 



Total length, 56 mm. ; length to base of caudal fin, 43 mm. ; length to 

 base of anal, 27 mm. ; length to base of ventral, 19 mm. ; length to base 

 of pectoral, 10 mm. ; length of head, 10 mm. ; interorbital width, 7.5 mm. 



This species need only be compared with the 0. affinis of Steindachner, 

 which is found near to Rio de Janeiro. That species has a posteiior 

 tuberosity of the occipital plate which is wanting in this species, and 

 Steindachner represents only one entire plate between the occipital and 

 the base of the dorsal spine. This region is more depressed in the 0. 

 flexilis, and the body is considerably more compressed, from the dorsal to 



PROG. AMER. PHILOS. SOC. XXXIII. 144. M. PKINTED MARCH 5, 1894. 



