eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 259 



(not counting the coalesced vertebrae); adipose lid covering almost the entire eye; 

 fontanels both large, the frontal fontanel becoming linear in front. 



A series of valvular organs on the roof of the mouth; the first a cushion about 

 as broad as long, with a transverse ridge in front and two blunt papillae near its 

 posterior edge, a blind pocket extending under it from behind; the second valve 

 consisting of a pair of soft flaps on the sides of the roof of the mouth, extending 

 obliquely downward and backward; the third a pair of triangular cushions, the 

 point extending forward and the base extending backward, free; the fourth a trans- 

 verse membrane with three pendant lobes in the middle; a pair of short papillated 

 flaps between the third and fourth valves. No tongue; a series of slender papillae 

 across the floor of the mouth in front of the gills, and opposite the anterior margin of 

 the triangular cushion; sides of the mouth in front of the gills with oblique series of 

 papilla?. Two air-bladders, connected by a slender thread only, the anterior about 

 as large as the eye, the posterior very delicate, large, straight, and conical, reaching 

 to the anus, 2.5 in the length. Alimentary canal about equal to the length without 

 the caudal, with eleven cceca; a highly muscular gizzard-like stomach with longi- 

 tudinal ridges extending into the lumen. The alimentary canal contains much 

 sand, which suggests trituration in the muscular stomach. 



118. Bivibranchia protractila sp. nov. (Plate XXXIII, figs. 1-5.) 



Type, 115 mm. Bartica sand-bank. (Carnegie Museum Catalog of Fishes 

 No. 1873.) 



Cotypes, eight specimens, 58-67 mm. Bartica sand-bank. (C. M. Cat. No. 

 1874a-c; L U. Cat, No. 12158.) 



Cotypes, eighteen specimens, 77-110 mm. Rockstone sand-bank. (C. M. 

 Cat. No. 1875a-c; I. U. Cat. No. 12159.) 



Cotypes, three specimens, 22-115 mm. Crab Falls. (C. M. Cat. No. 1876; 

 I. U. Cat. No. 12243.) 



Head 3.6; depth 4.6-5; D. 11; A. 9; scales 7 or 8—55 to 60—3 or 4; V. 11; 

 P. 17; eye equals snout, 3.2 in the head, .8-1 in the interorbital. 



Very similar to Albula vulpes. Dorsal and ventral profiles equal and gently 

 arched; profile of head slightly arched, the head subtriangular in cross-section, 

 flat above, its sides sloping toward its ventral edge; predorsal area broad, without 

 a regular median series of scales; belly broad and rounded, without a regular 

 median series of scales. Occipital process 6 in the distance from its base to the 

 dorsal. Snout pointed, much more so in the very young, the mouth very narrow, 

 less than half the width of the interorbitals. Upper jaw greatly protractile, the 



