118 MEMOIRS OF THE CARNEGIE MUSEUM 



(histrix of Schomburgk) ; sides of tail banded, lower surface of tail marbled; a small 

 black spot near the middle of the belly. 



Paratrygon Dumeril. 

 Paratrygon Dumeril, Hist. Nat. Poiss., I, 1865, 594. 

 Disceus Garman, Proc. Bost. Soc. Nat. Hist., 1877, 208. 



Type, Raja orbicularis Bloch and Schneider. 



This genus is distinguished from Potaniotrygon, among other characters, by the 

 absence of papillis in the mouth and by the smaller number of teeth. 



2. Paratrygon orbicularis (Bloch and Schneider). 

 " Aiereba" Marcgrave, in Piso, De Indise, etc., 1658, 175 (copied by Jonston, De 



Pise, pi. 38, fig. 6, and Willughby, 68, pi. 101, fig. 2). 

 Raja orbicularis Bloch and Schneider, Syst. Ichth., 1801, 361. 

 Trijqon orbicularis GIjnther, Catalogue, VIII, 1870, 482 (copied). 

 Trygon strongyloptera Schomburgk, Fishes Brit. Guiana. II, 1842, 183, pi. 22 



(Rio Branco). — Muller and Troschel, in Schomburgk, Reisen, III, 1848, 642 



(Rupununi; Takutu; Rio Branco). — GtJNTHER, Catalogue, \'III, 1870, 476 



(copied) . 

 Trygon aiereba Dumeril, Hist. Nat. Poiss., I, 1865, 592 (Brazil). 



No specimens were secured. 



Disk ovate, scarcely longer than broad; eyes very small; plain or with un- 

 dulating stripes. 



Class TELEOSTOMI. 



Key to the Orders of Teleostomi found in the Fresh-w.\ters of Guiana. 

 a. Weberian ossicles present; the anterior vertebroe coalesced. A single rayed dorsal fin,usuallyfollo\ved 

 by an adipose fin. 

 b. Skin nakedor with bony plates; maxillary rudimentary, forming the base of abarbel..Nematognathi. 

 66. Scales well-developed (rarely naked); maxillary not forming the base of a barbel. 



c. Body not eel-shaped (an adipose fin usually present) Heterognathi. 



cc. Body elongate, more or less eel-shaped, the anal fin very long Glanencheli. 



aa. No Weberian ossicles; the anterior vertebrae not united. 



d. Air-bladder connected with the alimentary canal by an open duct; ventral fins abdominal; no 

 spinous dorsal. 



c. A mesocoracoid; body not eel-shaped Isospondyli. 



ee. No mesocoracoid; parapophyses coossified with centra. 

 /. Body eel-shaped, no paired fins; no separate caudal. 



g. Gill-opening single, ventral; premaxillaries normally developed Symbranchii. 



{gg. Gill-openings not ventral; prema.xillaries rudimentary or wanting. Apodes.)^ 



//. Body not eel-shaped; paired fins; a well-developed caudal fin Microcyprini. 



^Muller and Troschel (Schomburgk, Reisen, III, 1S4S, 639) record Gymnothorax ocellatus from 

 plantation drains, and the fresh-water eel probably enters the Guiana rivers at times. 



