OSTARIOPHVSI 



579 



As an example of phytophagous types may be mentioned 

 the Moon-Fish of the Nile {Citlmrinus geoffroiji), 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. Gill-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 Eeinhardt. The. 

 few genera and species (about 30) 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 : Stemopygus, Eigenmannia, Sternarchas, Bham- 

 phosternarchus, Rhamphichtliys, Steatogenys. 



B. No cranial fontanelle ; maxillary bone very small ; anterior nostril 



on the upper lip ; vent on the throat. 

 a. Body scaly : Carapus. 

 h. Body naked ; an electric organ : Gymnotus. 



The mouth is small or very small, and the modifications of 

 the snout in the' genera Sternarclius 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 (Stemojjygus) 

 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. 



^ On the anatomy of the Characinidae, cf. Sagemehl, Morphol. Jahrb. x. 1885, 

 p. 102, and xil. 1887, p. 307, and Rowntree, Tr. Linn. floe. 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. 



^ Cf. Eeinhardt, Arch. f. Nalurg. 1854, p. 159. 



