318 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loi 



Host. — Paralichthys calif ornicus (Ay res), California halibut. 



Location. — Intestine. 



Types. — Holotypes and paratypes, U.S.N.M. Helm. Coll. No. 

 37142. 



Discussion. — The name labiatus is from labium, lip, and refers to 

 the preoral lip (ol, pi. 12, figs. 1, 2), which is not present in any 

 other species in the genus. Uncommon features are the posterior 

 location of the mouth, the reduced and contiguous vitellaria, the 

 long excretory vesicle, the curved cecum, and the long cirrus sac. 

 The species most similar to B. labiatus seems to be B. karvei 

 Bhalerao, 1937, from Belone in the Indian Ocean. The two species 

 agree in small body size, mouth posterior to midbody, and cirrus 

 sac reaching anterior to midbody ; but differ in that B. karvei has 

 vitellaria in two widely separated groups, does not have a recurved 

 cecum, lacks the preoral lip, and has smaller eggs. B. magyiaceto^ 

 bulum Nagaty, 1937, from Belone cho7'a77i, in the Red Sea, re- 

 sembles and differs from B. labiatus in the same respects except 

 that its cirrus sac is relatively shorter. It may be found that 

 B. karvei and B. magnacetabuluin are a single species. 



The occurrence in Belonidae of species of trematodes apparently 

 most similar to a species occurring in sinistral flat fishes (Bothi- 

 dae) suggests the host distribution of the species of Steganoderma 

 (Manter, 1947, p. 312). Neither the ecology nor the phylogeny 

 of these families of fishes indicates any relationship that would 

 be suggested by their trematode parasites. 



Order PROSOSTOMATA 

 Family OPECOELIDAE 



Genus OPECOELUS Ozaki, 1925 



OPECOELUS ADSPHAERICUS, new species 



Plate 12, Figures 3-5 



Description (based on about 60 specimens with measurements 

 on 7 individuals selected for size range). — Body elongate, cylin- 

 drical, smooth, 1.336 to 4.004 mm. long by 0.167 to 0.409 mm. in 

 greatest width. Oral sucker 0.084 to 0.146 in diameter ; acetabulum 

 0.112 to 0.255 mm. in diameter. Sucker ratio 1 :1.33 to 1.66. Acetab- 

 ulum protuberant; with three pairs of short, rather incon- 

 spicuous, lobelike, simple papillae (ap, pi. 12, fig. 4), barely dis- 

 cernible when retracted. Often only lateral views of the suckers 

 are presented; measurements of depths rather than transverse 

 diameters give similar sucker ratio. Forebody 0.197 to 0.511 

 mm. or about one-fifth to one-eighth body length. Posttesticular 



