666 FISHES. 



Extinct; developed in the chalk and extending into 

 tertiary formations : Dercetis (with the upper jaw longest), 

 Zeptotrachelus, Pelargorhynchus, PlintJwphorus, SaurorJiamphus 

 (with the lower jaw longest), JEuryplwlis ; Ischyroc&phalus (?). 

 The latter genus, from cretaceous formations of Westphalia, 

 is said to have two dorsal fins. 



Twenty-Ninth Family — Gymnotid^. 



Head scaleless ; barbels none. Body elongate, eel-shaped. 

 Margin of the upper jaw formed in the middle by the inter- 

 maxillaries, and laterally by the maxillaries. Dorsal fin absent 

 or reduced to an adipose strip ; caudal generally absent, the tail 

 terminating in a point. Anal fin exceedingly long. Ventrals 

 none. Extremity of the tape^'ing tail capable of being repro- 

 duced. Vent situated at, or at a short distance behind, the 

 throat. Humeral arch attached to the skull. Bibs well de- 

 veloped. Gill-openings rather narrow. Air-bladder present, 

 double. Stomach with a coscal sac and pyloric appendages. 

 Ovaries with oviducts. 



Eel-like freshwater fishes from Tropical America. 



Sternarchus. — Tail terminating in a distinct small caudal 

 fin. Teeth small. A rudimentary dorsal fin is indicated by an 

 adipose band fitting into a groove on the back of the tail ; it is 

 easily detached, so as to appear as a thong-like appendage fixed 

 in front. Branchiostegals four. 



Eight species, some have the snout compressed and of 

 moderate length, like St. Bonapartii from the Pdver Amazons ; 

 others have it produced into a long tube, as St. oxyrhynchus 

 from the Essequibo. 



Ehamphichthys. — Caudal fin none ; teeth none ; no trace 

 of a dorsal fin. No free orbital margin. 



Six species, of which, again, some have a tubiform snout, 

 whilst in the others it is short. 



