eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 399 



similar prongs; lower jaw with two or four prongs directed forward; cheeks almost 

 entirely covered by the suborbitals; gill-membrane free, from the isthmus; gill- 

 rakers similar on the two limbs, strong, few, long; pharyngeals with short, stiff 

 rakers; scales small, cycloid; dorsal over origin of anal, which is very long, of forty- 

 two to fifty-seven rays; pectorals overlapping ventrals; breast flat; tongue free. 

 Lateral line complete; alimentary canal short. 



254. Roeboides thurni sp. nov. (Plate LX, fig. 2.) 



Type, 104 mm. Rockstone sand-bank. (Carnegie Museum Catalog of 

 Fishes No. 2149.) 



Cotypes, four specimens, 45-115 mm. Rockstone sand-bank. (C. M. Cat. 

 No. 2150a-*; I. U. Cat. No. 12320.) 



Cotypes, nine specimens, 63-87 mm. Crab Falls. (C. M. Cat. No. 2151a-d; 

 I. U. Cat. No. 12321.) 



Head 3.6-3.75; depth 2.75-3.2; D. 11; A. 47-51, most frequently 48 or 49; 

 scales 17 to 19-72 to 80-10 to 13; eye 1-1.3 in the snout, 3.3-4 in the head, 1 in 

 the interorbital. 



Elongate; profile oblique, nearly straight to base of the occipital process, 

 then abruptly rising in an arch to the dorsal; preventral area rounded, without 

 a regular median series of scales; post-ventral area with a median keel; predorsal 

 area narrow, the median line in part naked ; about thirty scales between the dorsal 

 and the occipital crest; occipital crest reaching four-tenths of the way to the dorsal; 

 fontanel reaching to above the anterior margin of the eye. 



Opercles, suborbitals, and bones of the head wrinkled. Middle of opercle 

 drawn out into a flat spine. Snout pointed, premaxillary horizontal, meeting 

 the maxillary at an angle; premaxillary-maxillary border 2 in the head; maxillary 

 with about eight stout conical teeth with divergent points; premaxillary with 

 several conical thorns directed outward and forward, of which the anterior 

 is the largest, also two irregular series of small conical teeth ; lower jaw with thorns 

 directed forward and outward and a single series of teeth, of which the sixth tooth 

 is the largest, the first next in size and the remainder (about twenty) small, conical. 



Gill-rakers 7 + 10. 



Scales small, cycloid, without strife. Fins naked; lateral line straight. 



Origin of dorsal in advance of the middle, the fin small, the highest ray 4 in 

 the length; caudal small, the lobes 4 in the length; anal very long, slightly emar- 

 ginate, its origin equidistant from the snout and its end, a little nearer to the snout 

 than to the dorsal; ventrals reaching anal; pectorals beyond the middle of the 

 ventrals. 



