20 Field Columbian Museum — Zoology, Vol. V. 



i 



<S. Rhamdia Bleeker. 



Rhamdia Bleeker, Ichth. Arch. Ind. Siluri., 1858, 1Q7. (Type, Pime- 

 lodus quelen Quoy & Gaimard.) 



Body more or less elongate; head not especially widened; oc- 

 cipital process small or wanting, not reaching the dorsal plate; 

 fontanelle variously developed, not continued backward beyond 

 the eye, except in the young; young usually with two bony bridges 

 across the fontanelle, the one behind the eye the other in front of 

 the occiput ; in old specimens the entire fontanelle becoming obliter- 

 ated; adipose fin very long, adnate for its entire length to the back; 

 posterior nostril without a barbel; barbels 6. 



Several species of this genus are recorded from Mexico, but the 

 most of them probably occur south of the Isthmus of Tehuantepec. 

 This group of fishes is not well known. 



KEY TO THE SPECIES OF RHAMDIA. 



PAGE 



a. Head 3^ in length of body; anal rays 10 . . oaxacce 20 



aa. Head 4 to 5 in length of body, 

 b. Head 4 to \% in length of body, 

 c. Anal rays 12, or 13 ; adipose fin 3^ in body ; 



eye 2]/ 2 in interorbital area; head 4% laticauJa 21 



cc. Anal rays 9 or 10. 



e. Eye large, 5^3 in head brachyptera 21 



ee. Eye small, 7 ]/ 2 to 8 in head [wagneri] 22 



bb. Head 5 ; depth 6 ; anal rays 13 hypschira 22 



16. Rhamdia oaxacce Meek. Bagre. 



Rhamdia oaxacce Meek, Field Col. Mus. Pub. 65, 1002, 74; Cuicatlan. 



Streams of Mexico on the Atlantic side south of Vera Cruz. (Otopa; 

 Cordoba; Rio Blanco; Motzorongo; El Hule; Obispo;. Perez.) 



Head 3^; depth 53-3 ; D. 1, 6; A. 10. Body slender, stout ante- 

 riorly, compressed posteriorly; head large, flat, narrowed forward; 

 interorbital space 3 in head ; eye high up, small, its diameter 6^4 in head ; 

 occipital process 4^2 in head; width of mouth 2 in head; teeth in 

 jaws in bands; maxillary barbel reaching to middle of base of adipose 

 fin (slightly shorter in largest specimens, 6^ inches in length) ; mental 

 barbel reaching § distance to base of pectoral; postmental to just 

 past base of pectoral ; humeral spine extending to about )/$ length of 

 pectoral fin, covered with a membrane; gill rakers 3 + 7; origin of 

 dorsal fin slightly nearer tip of snout than first anal ray, its margin 

 rounded; origin of adipose fin at tips of dorsal rays, when fin is deflexed 

 and extending to opposite tips of depressed anal fin ; origin of anal 



