SOUTH AMERICAN NEMATOGNATHI. 33 



Orbit 3-3\ in the interorbital. Anterior half of occipital 

 slightly tnmid, the occipital sometimes having obscure 

 X-shaped ridges which are continued as tAVO parallel ridges 

 on the nuchal plates. 



Soft parts of the mouth in an oval depression; teeth fine, 

 numerous; barbels obsolete. Region between mouth and 

 pectoral fins Avith marginal plates only in the young, with 

 irregular polygonal plates in the adult. 



Belly with two series of plates, each with a median keel. 

 Anal x^late arrow-shaped, a small unpaired plate before it; 

 an elongate plate before the anal fin. Dorsal plate elongate, 

 separating one or two paired plates; six or seven paired 

 plates between the dorsal plate and the occipital, Sides of 

 the body covered with two series of obscurely keeled plates 

 which coalesce above or slightly behind the anal; 20-22 

 paired plates between the dorsal and caudal fins. 



Distance of dorsal fin from tip of snout 2-2^- in the length; 

 dorsal fin about three times as high as long, the first ray 

 highest. 



Outermost caudal rays elongate, varying from the length 

 of the snout to much longer than the head. 



Anal fin well developed, inserted under third or fourth 

 dorsal ray, little lower than dorsal fin. 



Pectoral fins short, not reaching the ventrals, ventrals not 

 to the anal fin. 



Light olivaceous to dark brown, the raj^s of all the fins 

 barred; each caudal lobe with a narrow, dark brown stripe, 

 sometimes with a few flecks of light across it; base of caudal 

 sometimes with a large dusky spot. 



Length of head to end of- occipital plate 2|-3j in the 

 length. 



D. 7; A. 6; V. 5: P. 7; lat. 1. 30-34. 



3. Farlowella knerii (Steinducimer). 



4. Farlowella oxyrrhynchus (Kner). 



2d Ser., Vol. II. Issued August 18, 1889. 



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