320 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loi 



eggs (54 to 65 fx by 30 to 38/i for minor as compared with 63 to Ibfi 

 by 40 to 45ja for sebastodis) . He expressed the view that egg 

 measurements differed considerably between living and preserved 

 specimens, yet most descriptions do not indicate whether measure- 

 ments are made on living or fixed material. Also, it seems unusual 

 that Yamaguti should claim considerably larger egg sizes for pre- 

 served material as compared with living. Actually, his living egg 

 sizes for O. 7ninor agree well with measurements on two pre- 

 served specimens of 0. minor sent to one of us (Manter) by Yama- 

 guti several years ago. Thus, O. minor can be distinguished from 

 0. sphaerictts by its longer acetabular papillae and smaller eggs 

 (72 to 81/A by 41 to Al/x for sphaericus) . The rather small speci- 

 mens from a "black eel" reported as "probably" 0. sphaericus by 

 Yamaguti (1940 p. 73) would seem to be doubtfully that species. 

 Their sucker ratio and egg sizes are much more like O. minor. 



The corrections by Yamaguti mentioned above make O. sebas- 

 todis more like O. sphaericus. Egg sizes agree as well as body pro- 

 portions. The only difference discernible from descriptions is one 

 of body size (1.6 to 3.4 mm. length for sebastodis, 4.3 to 8.25 mm. 

 for sphaericus) . Until and unless further constant differences can 

 be found, O. sebastodis should be considered a synonym of 0. 

 sphaericus. 



Opecoelus adsphaericus differs from 0. minor only in having 

 short, inconspicuous acetabular papillae and a more anterior 

 genital pore. Even when the acetabulum is greatly extended the 

 papillae are usually very short in O. adsphaericus. In only 3 speci- 

 mens of more than 60 did the papillae seem to be at maximum ex- 

 tension measuring up to 0.036 mm. in length. In two specimens of 

 0. minor available for study, each of which was almost exactly 

 the size of the above specimens of O. adsphaericus, the papillae 

 measured 0.050 and 0.072 mm., while Yamaguti states they reach 

 0.118 mm. His figure shows them about as long as the depth of 

 the acetabulum itself, a condition never approached in O. ad- 

 sphaericus. Also, in O. minor the papillae have a thick outer 

 layer of cuticula. The two species agree in shape and location of 

 reproductive organs and in egg size. Sucker ratios are difficult 

 to compare, as Yamaguti's original figures indicate a ratio of 1 :1.8 

 for 0. minor but his fig. 46 (1934), which he later (1940) claimed 

 to be O. minor rather than O. sebastodis as labeled, shows a ratio of 

 more than 1 :2. We do not feel it possible to identify our specimens 

 as 0. sphaericus (= 0. sebastodis) because of two differences: 

 O. adsphaericus has a genital pore opposite the anterior half of 

 the esophagus and an egg size of 49 to 59 fi by 26 to 24/a (as com- 

 pared with 72 to 81/i, by 44 to 47/ia) . Our specimens are consider- 



