666 FISHES. 



Extinct; developed in the chalk and extending into 

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

 Lqjtotrachelus, PelargorhyncJius, Plint]ioj)horus, Smcrorliamplms 

 (with the lower jaw longest), Eurjiplwlis ; Ischyrocephalm (?). 

 The latter genus, from cretaceous formations of Westphalia, 

 is said to have two dorsal fins. 



Twenty-Ninth Family — Gymnotid.e. 



Head seal cl ess ; harhels none. Body elongate, eel-shaiJed. 

 Margin of the upper jaw formed i?i the micMle hy the inter- 

 maxillaries, and latercdly hy 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 ta-jwring tail capable of being repro- 

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

 throat. Htivieral arch attached to the slcull. Bibs well de- 

 veloped. Gill-openings rather narroio. Air-bladder 'present, 

 douhle. Stoviach ivith a ccecal sac and pyloric appendages. 

 Ovaries tvith oviducts. 



Eel-like freshwater fislies 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 thongdike appendage fixed 

 in front. Branchiostegals four. 



Eight species, some have the snout compressed and of 

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

 otliers have it produced into a long tube, as St, oxyrhynchus 

 from the Essecpiiljo. 



Rhamphichthys. — 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. 



