206 siLrRTD^i. 



81. OXYDORAS. 



Oxydoras, sr et Doras, sp., Kner. 



Doras, Bleek Nederl. Tt/dsschr. Dierh. 1863, p. 84. 



Adipose fin short, very distinct ; dorsal with a strong spine and 

 with six soft rays ; anal short. Teeth rudimentary, sometimes pre- 

 sent in the lower jaw only, sometimes entirely absent. Cleft of the 

 mouth rather narrow ; barbels six, fringed and united at the base by 

 a fold of the skin. Eyes of moderate size. Xeck with broad dermal 

 bones ; a large humeral process above the pectoral fin ; a series of 

 shields along the middle of the side of the body and tail, each shield 

 with a compressed, prominent, curved central spine. Gill-openings 

 of moderate width, not extending downwards to the throat. Ventral 

 fins with seven rays, inserted behind the dorsal. 



Rivers of South America flowing into the Atlantic. 



1. Oxydoras carinatus. 



Silurus carinatus, L. Syst. Nat. i. p. 504 ; Bl. Schn. p. 108. 

 Doras oxvrhynchus, Valenc. in Humb. Observ. Zool. ii. p. 184. 



carinatus, Cm: # Val. xv. p. 288. pi. 440 (bad). 



Oxydoras carinatus, Kner, Sitzgsber. Wien. Acad. 1855, xvii. p. 144. 



D. 1/6. A. 12-13. P. 1/9. V. 7. L. lat. 33. 



Adipose fin short. Lateral shields small, half covered with thin 

 •skin ; the upper and lower halves of each shield terminate behind in 

 a simple or bifid or trifid spine. Tail without shields on its upper 

 and lower surfaces. Humeral process striated, obtuse behind, twice 

 as broad as, and extending nearly to the hinder third of, the pectoral 

 spine. Eye of moderate size, its diameter being rather more than its 

 distance from the posterior nostril. The bases of the six barbels are 

 united by a broad membrane fringing the lower jaw ; the maxillary 

 barbel is provided with a series of from six to eight smaller tentacles 

 along its basal half, and extends to the eye ; the mandibulary are 

 only one-third as long, and have their lower surface covered with 

 papillae. Lower jaw with two patches of minute teeth in front*. 

 Uniform greenish olive above, whitish below. 



Surinam. 



a. Adult : 13 inches long. Surinam. 



h-c. Fine specimens. Essequibo River. Purchased of Mr. Ehrhardt. 



2. Oxydoras humeralis. 



Doras humeralis (Heckel). Kner. Sitzunqsber. Wien. Acad. 1855, xvii. 

 p. 140. fig. 6. 



D. 1/6. A. 12. P. 1 s. v. 7. L. lat. 32. 



The lower profile of the head ascends in a curve similar to that 



in which the upper descends ; snout pointed. Adipose fin short and 



small. Lateral shields rather small and narrow, each provided with 



a series of marginal spines. Tail without shields on its upper and 



* Our specimen a. has two or three minute teeth on the right-hand side in the 

 upper jaw; the other side is without any teeth. 



