1886.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 359 



a distinct subgenus or possibly genus. For this group the name Ath- 

 lennes* has been given. But one species is known. Its characters are 

 given in contrast with those of the species of Tylosurus in our analjsis 

 of the latter. 



Genus III. POTAMOERHAPHIS. 



POTAMORRHAPHis Gunther, vi, 1866, 256 (tceniata). 



This genus is well distinguished from the others in the family by the 

 form of its dorsal and caudal fins. Its single known species inhabits the 

 fresh waters of Brazil and Guiana. 



ANALYSIS OF SPECIES OF POTAMOKEHAPHIS. 



a. Dorsal rays 30 to 34 ; aual rays 25 to 30 ; lat. 1. 180 ; trunk tetraedral, as broad as deep ; 

 tail long, strongly compressed, without keel; beak broad, strongly depressed, 

 the lower jaw broader and longer than upper; teeth small; eye small, 24- in 

 postorbital part of head ; maxillary half hidden ; veutrals far back, inserted 

 midway between base of pectoral and caudal ; anterior rays of dorsal very low, 

 those of anal considerably elevated. A dusky lateral band on sides. 



GUIANENSIS, 21. 



21. Potamorrhaphis guiauensis. 



Belone guianensis "Schomburgk, Fish, Guiana, 1841, ii, pi. 1, 131" (Guiana: 



name only?). 

 Tylosm'us guianensis Miiller & Trosehel, "Schomburgk, Keise Brit. Guiana, 



ill, 626,1843" (Guiana). 

 Belone scolopacin a Cuv. & Val., xviii, 428, 1846 (Rio de la Mana, Cayenne); 



Giinther, vi, 256 (copied). 

 Belone tceniata Giinther, vi, 256, 1866 (Rio Capin, Brazil). 

 Potamorrliaphis tceniata Steindachner, Ichth. Beitr., iii, 68, 1875 (Amazon 



River at Teff^, Villa Bella, Porto do Moz, Sautarem, Gurupa, Hyavaiy 



River, Lake Mauacapuru, etc.). 



Hahitat. — Rivers of Guiana and Brazil. 



Head 2'^; depth 8 in head; breadth at pectoral 8|-; D. 34 ; A. 30; Lat. 1. 

 about 174; scales before dorsal 108; length (specimens from Itaituba) 

 8i inches. 



Body slender, subquadrate in section, broad anteriorly; tail long and 

 slender, much compressed, the lateral line not forining a keel and not 

 black. 



Jaws very long and slender, the lower much broader than the upper 

 and somewhat longer; length of upper jaw from eye 3f times in length 

 of body and 2^ times length of rest of head. Mouth closing completely. 

 Eye small, its diameter 1| in interorbital space, 2-J in postorbital part of 

 head and 10 in snout. Teeth very small and slender (in conii)arison 

 with those of most species of Tylosurus). Teeth, bones, and scales ap- 

 parently not green; maxillary not nearly covered by the preorbital. 



Interorbital space with a deep naked channel, on each side of which 

 is a slight ridge; vertex somewhat convex; superciliary ridge rather 

 sharp; bones of head little striate; no distinct fold of skin across edge 

 of preopercle; cheek entirely scaled, its scales moderate in size, scales 

 on body comi^aratively large. 



^AdXevvfjg, "without mucosity," an epithet applied by early authors to their /^f/'ov?/ 

 or Acus, according to Valenciennes. 



