eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 193 



cc. Maxillary barbel extending to base of pectoral; eye 4.5 in the head in the adult (3 in the young), 

 2.75 in the snout (1.5 in young); teeth well-developed in both jaws; snout pointed; 



mouth 1-1.5 in distance between gill-openings carinatus. 



bb. Lateral plates of anterior part of body rudimentary or very small, increasing in size backward. 

 d. Teeth of the lower jaw minute, in two separate patches; differing from carinatus largely 



in the rudimentary anterior plates micropceus. 



dd. Teeth of the lower jaw large, brown-tipped, in a single median patch; maxillary barbel ex- 

 tending beyond origin of pectorals; snout bluntly decurved; pectorals extending to 

 ventrals; base of dorsal dark; a light band along the lateral hooks, bordered above 



and below by darker, which is most intense on base of caudal leporhinus. 



aa. A large foramen on either side of the juncture between dorsal plate and occipital process; dorsal with 

 a conspicuous black spot. (Hassar.) 

 c. Maxillary barbel extending to base of pectoral; orbit oval; snout long, conical; pectoral spine reach- 

 ing ventrals; dorsal spine with hooks on the basal half of the anterior margin; humeral 



process elongate, its upper margin not greatly arched notospilus. 



(ee. Maxillary barbel to below posterior part of the eye; orbit o'vate with a narrowing forward exten- 

 sion; snout slender; origin of orbit behind the middle of the head; pectoral spine not 

 reaching ventrals; dorsal spine with hooks along the basal two-thirds or three-fourths of its 

 anterior margin; humeral process spatulate, its dorsal margin much curved. 



/. Scapula covered with skin; dorsal spot not extending to tip of the membranes orestes. 



//. Scapula granular; black spot extending to upper margin of dorsal membranes wilderi.) 



62. Hemidoras microstomus sp. nov. (Plate XVIII, fig. 2.) 



Hemidoras microstomus Eigenmann, Repts. Princeton Univ. Exp. Patagonia, III, 



1910, 394 (name only). 



Type, 52 mm. Rockstone. (Carnegie Museum Catalogue of Fishes No. 1650.) 



Cotypes, twelve specimens, 35-51 mm. Crab Falls. (C. M. Cat. No. 1651 

 a-b; I. U. Cat. No. 12040.) 



Cotype, one specimen, 52 mm. Rockstone. (I. U. Cat. No. 12039.) 



Head 3.75-4.2; depth 4.33-5.5; D. 1,6; A. 10-12; lateral plates 26-32; eye 

 2.5-2.66 in the head, 1-1.33 in the snout; interorbital 1-1.66 in eye. 



Profile from dorsal to above eye straight, then descending rapidly; the snout 

 very blunt, rounded; lower jaw much shorter, included; fontanel elliptical, little 

 longer than eye, not continued as a groove; top of head convex. Width of mouth 

 equal to half the distance between gill-openings. Teeth very feeble, if present. 

 Maxillary barbels reaching gill-openings, or a little shorter; distance of dorsal 

 spine from tip of snout 2.75-3 in the length. 



Dorsal spine as long as the head or a little longer, with serrae on the basal half 

 of the anterior margin and entire length of posterior margin. Pectoral spine a 

 little longer or shorter than the dorsal spine, reaching the ventrals; base of adipose 



