112 OSTARIOPHYSI. 
Supraoccipital with a median ridge and bordered posteriorly by a single scute. Dark spots on head, 
body, and fins. 
Hab, Panama to Paraguay. 
This species, which attains a length of 350 mm., is known to range from Venezuela 
to Paraguay. It has also been recorded by Kner and Steindachner (Abhandl. 
Bayer. Akad. x. 1865, p. 60) from Panama. The Panama specimens are said to 
differ from the typical P. guacari in having more numerous teeth (40 on each side), a 
lower occipital keel, &c., but the probable explanation is that Kner and Steindachner 
had examples of the true P. guacari and compared them with specimens of P. verres, 
Cuv. & Val., a species which has not usually been distinguished from P. guacari, but 
which differs from it in the fewer teeth, higher occipital keel, &c. 
2. ANCISTRUS, Kner. 
Ancistrus, Gill, Ann. Lyc. N. York, vi. 1858, p. 407; Regan, Trans. Zool. Soc. xvii. 1904, p. 221. 
Similar to Plecostomus, but operculum and interoperculum independently movable, the latter usually with a 
group of spines or bristles which can be everted. 
Thirty-one species from Tropical America. 
1. Ancistrus aspidolepis, Giinth. 
Ancistrus aspidolepis, Regan, Trans. Zool. Soc. xvii. 1904, p. 230. 
DorsalI 7. AnalI4. Scutes all strongly keeled, 25 in a longitudinal series. Interoperculum armed with 
a few short spines. Small dark spots or vermiculations on head, body, and fins. 
Hab. Panama, Veragua. 
Total length 280 mm. 
3. CHAETOSTOMUS, Tschudi. 
Chetostomus, Regan, Trans. Zool. Soc. xvii. 1904, p. 244. 
Similar to Ancistrus, but the snout with a naked margin. 
Fifteen species, chiefly from the Andes of Peru, Ecuador, and Colombia, but extending 
into Venezuela and Panama. 
1. Chetostomus fischeri, Steind. 
*hetostomus fischeri, Steind. Denkschr. Ak. Wien, xli. 1879, p. 164, t. 4. fig. 9. 
Dorsal 18. AnalI5. 23 to 24 scutes in a longitudinal series, none of them keeled. Interoperculum armed 
with 1 or 2 short spines. Head and anterior part of body with little yellowish spots; fins spotted or 
clouded with blackish. 
Hab. Panama, Rio Mamoni. 
Total length 275 mm. 
