EIGENMANN: THE FRESHWATER FISHES OF BRITISH GUIANA 



225 



One specimen, 132 mm. Botanic Garden. (C. M. Cat. No. 1586a.) 



This species differs from Plecostomus plecostomus notably in color and in the 

 length of the mandibular ramus. 



Head 3; depth 5-5.5; D. 1,7; A. 1,4; scutes 25 or 26 + 1. Width of head 

 an orbital diameter less than its length, its depth about 2 in the length, 3.5 in the 

 snout; eye 6 in the head, interorbital 3; mandibular ramus 2 in the interorbital. 



Supraorbital slightly raised, a blunt median ridge on occipital forward to above 

 eye; occipital bordered by a single plate; some of the plates distinctly, but feebly, 

 keeled; ventral surface naked (except in the Ireng specimens, in which there are a 

 few minute granular plates between the pectorals). 



Dorsal spine variable, less than, or considerably longer than, the head, base of 



Fig. 34. Plecostomus hemiurus Eigenrnann. Type. C. M. Cat. No. 1544. 



dorsal equal to its distance from the caudal. Caudal oblique, emarginate, the 

 lower rays usually less than twice the length of the middle rays ; ventrals reaching 

 middle of anal; pectorals to second third of ventrals or beyond. 



Dark brown, with dark olive spots, smallest on the head, absent on the belly; 

 dorsal spotted along the basal half or near its tip ; caudal sometimes uniform dark 

 brown, its upper lobe sometimes colored like the dorsal, as well as the upper surface 

 of ventrals and pectorals. 



92. Plecostomus watwata (Hancock). (Plate XXVI, fig. 1.) 

 Hypostomus watwata Hancock, Zool. Journ., IV, 1829, 245 (Georgetown). 

 Hypostomus plecostomus mot of Linnaeus) Cuvier and Valenciennes, Hist. Nat. 



Poiss., XV, 1840, 489 (Maracaibo). 

 Hypostomus verves Cuvier and Valenciennes, Hist. Nat. Poiss., XV, 1840, 494 



(Cayenne). 



