REVIEW OF OPHIDIOID FISH GENUS OLIGOPUS — COHEN 3 



Bathystorreus Howell Rivero, 1934, p. 69 (type species by original designation 

 Benihocometes claudei Torre, 1930). 



Diagnosis. — Gill membranes separate. Chin barbel absent. 

 Live-bearing. Pelvic fins each with one ray, originating close to 

 level of posterior margin of preopercle and about an eye diameter 

 behind symphysis of cleithra; vertical fins continuous, covered proxi- 

 mally with thick, scaleless skin; pectoral fin entire, without separate, 

 elongated rays. Head partly naked, bearing dermal papillae; anterior 

 nostril tubular, located directly above upper lip; gill rakers 2 or 3; 

 tongue a massive structure with anterior, prowlike projection fitting 

 between 2 heads of geniohyoideus muscle. Branchiostegal rays 8. 

 Body relatively short, stubby; head not depressed, height greater than 

 ^vidth. Lateral line \vith 2 or more series, dorsal and ventral some- 

 times overlapping or parallel for entire lengths ; palatine lacking teeth ; 

 ventrally directed projection usually present at posteroventral section 

 of maxillary; posterior portion of maxillary expanded. Eyes well 

 developed. Body completely covered with small cycloid scales. 

 Lining of peritoneum pale in color. 



First neural spine low; neural spines 2, 3, 4 raised, followed by 

 series of low neural spines with more or less truncate tops (fig. 1). 

 Vertebrae 1 and 2 without ribs ; vertebra 3 with pair of antero ventrally 

 directed ribs; vertebrae 4-6 with postero ventrally directed ribs 

 articulating with centra; vertebra 7 with ribs attached, free or at 

 end of parapophyses ; vertebrae 8-10, 11 or 12 with ribs at ends of 

 parapophyses ; all other vertebrae lacking pleural ribs. 



Relationships. — Oligopus is a distinctive group of well-differentiated 

 species. The genus apparently represents a rather generalized type 

 of ophidioid, at least among the live-bearers, and this fact, along with 

 its relatively shallow-water habitat, suggests that, together with 

 Bythites, Oligopus may be close to the stem from which various 

 forms descended toward an abyssal habitat while others colonized 

 the coral reefs: Oligopus has affinities with fishes that dwell in both 

 areas. 



Among the reef inhabitants, Microbrotula, Grammonoides, and 

 Stygnobrotula are related to Oligopus; the former two even possess 

 the peculiar projection on the maxillary. None of the three genera, 

 however, displays the peculiar shortened and truncate neural spines 

 (fig. 1) that are characteristic of Oligopus; moreover, Microbrotula 

 has palatine teeth, and Bohlke (1957) has given a number of reasons 

 for separating Stygnobrotula from Eutyx (here considered a junior 

 synonym of Oligopus), most of which serve to separate Stygnobrotula 

 from the more inclusive genus Oligopus. Particularly important are 

 Bohlke's items 1, 2, 3, 4, 6, 7, 9, and 13 of his table 1, p. 3, to 



