192 MEMOIRS OF THE CARNEGIE MUSEUM 



Cotype, one specimen, 174 mm. Georgetown market ? (C. M. Cat. No. 

 1630.) 



Head 3.5; depth 6; D. 1,6; A. 12-14; lateral plates 38-39; eye 3.5-4 in head, 

 1.75-1.8 in snout; interorbital 2 in eye. 



Slender; depth equal to width; caudal peduncle broad, depressed, its depth 

 equal to half its width, less than the distance of the anal from the caudal ; fontanel 

 continued as a groove to the tip of the occipital process. A small foramen on 

 either side of the occipital process; no teeth; mouth nearly equal to the distance 

 between the gill-openings. Maxillary barbel reaching gill-opening in the young, 

 shorter in the adult. 



Lateral plates well-developed along the entire sides, each with a central hook 

 and a series of marginal spines, those above the median hook close-set; median 

 hook strongest on the plates, just behind the vertical from the anal; humeral 

 process short, its upper margin greatly arched. 



Dorsal and pectoral spines of about equal length, little shorter than the head, 

 the pectoral spine reaching to the middle of the ventrals or farther in the adult, 

 not much beyond the base in the young; pectoral spine serrate on both edges, the 

 teeth much stronger on the inner surface; dorsal spine with much feebler serrations; 

 adipose free behind, its base nearly or quite equal to the base of the dorsal exclusive 

 of the spine. A large pectoral pore. 



White beneath, uniform dark above; a pair of parallel bands on the caudal, 



the middle rays light. 



Hemidoras Bleeker. 



Doras Lacepede, Hist. Nat. Poiss., V, 1803, 116 (carinatus and costatus).— 



Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 13 (carinatus), not Doras Cuvier 



and Valenciennes. 

 Oxydoras Kner, SB. Akad. Wiss. Wien, XXVII, 1855, 142 (sp.). 

 Hemidoras Bleeker, Ichth. Arch. Ind. Prodr., I, 1858, 53 (stenopeltis) . 

 Hassar Eigenmann and Eigenmann, Proc. Cal. Acad. Sci., (2), 1, 1888, 158 (orestes). 



Type, Doras stenopeltis Kner. 



Barbels fringed; eye large. One or both jaws with teeth; numerous pectoral 

 pores. 



Key to the Guiana Species of Hemidoras. 



a. No foramen on either side of juncture between occipital process and dorsal plate. (Hemidoras.) 



b. Lateral plates of the anterior part of the body well-developed; teeth in the lower jaw small, in 



two patches. 



c. Groove of the fontanel not extending backward; maxillary barbel not reaching gill-opening. 



Eye 2.75 in head (1 in young); teeth very feeble, mouth half as wide as distance 



between gill-openings microstomus. 



