10 ACANTHOPTERYGII. 
I have examined numerous examples of this form from Presidio, Huamuchal, and 
Guayaquil, measuring from 110 to 280 mm. in total length. 
4, SICYDIUM, Cuv. & Val., 1837. 
Sicydium and Cotylopus, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, pp. 2205 & 2207. 
Oreogobius, Bouleng. Aun. Mag. N. H. (7) iv. 1899, p. 126. 
Body elongate, subcylindrical. Mouth wide, subterminal, the lower jaw the shorter ; lips thick ; both jaws 
with a series of numerous slender teeth, those in the lower jaw horizontal, sometimes completely hidden 
by the gum; an inner series of erect conical teeth in the lower jaw; palate toothless. Eyes small or of 
moderate size ; interorbital region moderately broad. Gill-openings of moderate width, nearly vertical, 
not produced forward below. Scales small, ctenoid. Two dorsals, with VI (V—VII), I 10-12 rays ; 
anal with I 9-11; caudal rounded; pectoral symmetrical, rounded; ventrals united to form a disc 
which is free from the body posteriorly, with a basal membrane which is folded to form a pit 
anteriorly. 
In the males the dorsal fins are more elevated than in the females, whilst the rays 
of the anterior dorsal are produced into long filaments. 
The genus comprises about thirty species from tropical rivers near the sea, three of 
which are found in Mexico and Central America. 
1. Sicydium salvini. 
Sicydium salvini, Grant, Proc. Zool. Soc. 1884, p. 159, t. 12. fig. 2°. 
Sicyopterus salvini, Jord. & Eigenm. Proc. U.S. Nat. Mus. 1886, p. 485 *. 
Cotylopus salvini, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2208 °. 
Oreogobius rosenbergii, Bouleng. Ann. Mag. N. H. (7) iv. 1899, p. 126°. 
Horizontal teeth of lower jaw conspicuous. Scales extending forward on the upper surface of head nearly 
to the interorbital region; abdomen completely covered with small scales; 68 to 76 scales in a 
longitudinal series. Dorsal VI,1 10. Anal 110. Body with broad irregular dark cross-bars and with 
a more or less distinct dark longitudinal band from pectoral to base of caudal; each scale with a dark 
spot at the base; dorsal fins dusky, the second usually with numerous small dark spots, which may 
unite to form a network; anal dusky in the male, in the female pale with a dark intramarginal stripe. 
Hab. Panama !.—WEsTERN Ecuapor ‘. 
Here described from five specimens, measuring up to 120 mm., including the types 
of the species and of O. rosenbergit. 
2, Sicydium gymnogaster. 
Sicydium gymnogastey, Grant, Proc. Zool. Soc. 1884, p. 158, t. 11. fig. 2 and t. 12. fig. 6°. 
Sicyopterus gymnogaster, Jord. & Eigenm. Proc. U.S. Nat. Mus. 1886, p. 485 ”. 
Cotylopus gymnogaster, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, p. 2207’. 
Horizontal teeth of lower jaw usually more or less completely concealed beneath a fleshy pad. Scales not 
extending forward on to the head; abdomen with a median naked area; 60 to 74 scales in a longitudinal 
series *. Dorsal VI, 110. AnalI10. Coloration as in S. salvini, but the fins without spots. 
* In three specimens the scales extend forward above to the level of the gill-opening, and in these I count 
66 to 74 in a longitudinal series. Usually the scales commence above the pectoral, and consequently this 
number is fewer. 
