REVIEW OF OPHIDIOID FISH GENUS OLIGOPUS — COHEN 13 



Oligopus diagrammus (Heller and Snodgrass) 



PLATES 1, 5 



Eutyx diagrammus Heller and Snodgrass, 1903, p. 224, pi. 19 (original description, 

 Galapagos, Tagus Cove, Albemarle Island, and Seymour Islands). — Bohlke, 

 1957, p. 3 (paratype of E. diagrammus compared with Stygnohrotula late- 

 hricola) . 



Study material. — Holotype, SU 6346 and paratype SU 7059 from 

 the Galapagos. The following from Guadalupe Island, Baja Cali- 

 fornia, Mexico: SIC 58-497 (1); SIC 58-493 (1); SIO 54-213A (1); 

 SIO 54-219 (1); SIO H53-169 (1); SIO 54-219A (6); SIO 60-14-61E 

 (2). Following from peninsular Baja California or closely adjacent 

 islands: SIO 61-272-61B, Espiritu Santo Island (3) ; SIO 61-227-61A, 

 Cape San Lucas (2); SIO 61-242-61 A (4); and SIO 61-249 (1), 

 Los Frailes. 



Counts and measurements. — Caudal 10; vertical scale rows be- 

 tween 100 and 115, very difficult to count. Vertebrae 49-53. (See 

 table 2 for a summary of measurements, and table 3 for counts.) 



Description. — Squamation: Patch of scales on top of head pos- 

 terior to interorbital. Patch of scales present on opercle and in front 

 of opercle extending anteriorly to a point less than eye diameter 

 behind eye. Dorsal and lateral scale patches appearing continuous 

 in some specimens and separated by scaleless area over lateral canal 

 in others (small size of scales and adherent mucous coating on head 

 make this a difficult character of which to be certain). Scale patch 

 posterior to hind margin of maxillary appearing to be continuously 

 connected with main opercular scale patch. 



Lateralis system: Lateral canal with 1 pore near upper angle of 

 opercle. Supraorbital canal with 1 pore in front of, and below, 

 anterior nostril. Infraorbital canal with 5 pores: 1 behind anterior 

 nostril; 2 along lip below posterior nostril; and 2 above posterior 

 expanded portion of maxillary. Preoperculomandibular canal with 

 8 pores: 2 at tip of dentary, 1 opening anteriorly, the other posteriorly ; 

 1 beneath lower lip close to level of posterior nostril (not shown in 

 fig. 4) ; 1 at about midlength of jaw (could not be found in holotype) ; 

 1 slightly ahead of posterior margin of maxillary; 1 slightly behind 

 same. Two elongate slits along posterior margin of preopercle. 



Circumorbital, interorbital, and opercular areas and snout bearing 

 scattered papiUae. Small dark papillae distributed on head but 

 thickly dispersed in particular on top of head and over adjoining 

 predorsal area of top of body. 



Lateral line marked by small papillae. One series of about 30 

 originating on head above opercle and, after slight irregular dip 

 behind opercle, extending posteriorly in straight line between midline 



