XX1 OSTARIOPHYSI 579 
As an example of phytophagous types may be mentioned 
the Moon-Fish of the Nile (Citharinus geoffroyi), with its feeble 
dentition, deep compressed body, and falciform dorsal fin; it is 
often represented on the monuments of the ancient Egyptians.' 
Fam. 2. Gymnotidae.—Mouth non-protractile, bordered by 
the praemaxillaries and the maxillaries, the latter sometimes 
much reduced; jaws usually toothed. Parietal bones united in 
a sagittal suture, or separated by a fontanelle; opercular bones 
well developed; symplectic present. Pharyngeal bones normal, 
with small teeth. Anterior ribs sessile, the posterior inserted. 
on transverse processes ; epipleurals and epineurals. Body much 
elongate, Eel-like, naked or scaly; dorsal fin absent or reduced 
to an adipose strip; anal very long; caudal rudimentary or 
absent ;” ventrals absent. Vent under the head or at a very 
short distance behind the throat. Gull-openings narrow. 
In spite of their external appearance, these fishes have 
nothing to do with the Eels; they are strongly modified, 
degraded Characinids, as first pointed out by Reinhardt. The 
few genera and species (about 50) are confined to the fresh 
waters of Central and South America. No fossils are known. 
Eight genera may be distinguished :— 
A. A cranial fontanelle ; maxillary bone larger than the praemaxillary ; 
anterior nostril on the upper surface of the head; vent below the 
head ; body scaly: Sternopygus, Eigenmannia, Sternarchus, Rham- 
phosternarchus, Rhamphichthys, Steatogenys. 
B. No cranial fontanelle ; maxillary bone very small; anterior nostril 
on the upper lip; vent on the throat. 
a. Body scaly: Carapus. 
b. Body naked ; an electric organ: Gymnotus. 
The mouth is small: or very small, and the modifications of 
the snout in the genera Sternarchus and Rhamphichthys recall 
those noticed among the Mormyridae. The air-bladder is 
divided into an anterior and a posterior part, united by a slender 
duct. The vertebrae vary in number from 70 (Sternopygus) 
to 240 (Gymnotus). Gymnotus is unique in this sub-order in 
having as many as 8 pterygials (actinosts) to the pectoral fin, 
as in Anguilla. 
1 On the anatomy of the Characinidae, cf. Sagemehl, Morphol. Jahrb. x. 1885, 
p. 102, and xii. 1887, p. 307, and Rowntree, 77. Linn. Soc. ix. 1903, p. 247. 
* The end of the tail, when injured, is easily reproduced. As in Lizards, the 
axis of the regenerated part is an undivided calcified tube. 
3 Cf. Reinhardt, Arch. f. Natury. 1854, p. 159. 
