370 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



from posterior edge of acetabulum to posterior end, not confluent between 

 testes, often overlapping the ceca ventrally but not dorsally. Colorless cel- 

 lular structures the same size and shape of vitellaria in forebody ("rudi- 

 mentary vitellaria"). Excretory pore subterminal, slightly dorsal; excre- 

 tory vesicle a straight tube extending to level of ovary. 



Comparisons. This species is probably most similar to Opegaster acu- 

 ta. Two constant differences are: more posterior genital pore in O. pente- 

 dactyla and more anterior anus in O. acuta. Opecoelus xenistii has very 

 similar acetabular papillae and terminal genital organs. Actually, al- 

 though named in a different genus, O. xenistii is possibly identical with 

 Opegaster pentedactyla. The difficulties in separating the genera have 

 been mentioned above. Opegaster pentedactyla is considered distinct from 

 Opecoelus xenistii because of more constant "rudimentary vitellaria," 

 smaller size, considerably larger pharynx, slightly smaller eggs, and 

 smooth testes. 



A number of specimens secured from a fish (B. verres), which died in 

 the ship's tanks, showed some variations probably due to their macerated 

 condition. They are slightly longer, more slender, with longer prepharynx 

 and esophagus, less conspicuous acetabular processes. One specimen 

 seemed to have but 3 acetabular processes. Because of agreement with O. 

 pentedactyla in other respects, the specimens were identified as that 

 species. 



Opegaster parapristipomatis Yamaguti, 1934 

 (Plate 37, fig. 43) 



Hosts: Trachinotus rhodopus (Gill) 



Selar crumenophthahnus (Bloch) 

 Location : Intestine 

 Locality: Chatham Island, Galapagos 

 Number: 6 in one, 15 in another of 2 hosts 



The differences between these trematodes and O. parapristipomatis 

 are considered too small to justify a new species. These differences are as 

 follows: my specimens (1.200 to 1.790 in length) are somewhat smaller 

 than the Japanese species which is 2.5 to 2.8 in length. The vitelline folli- 

 cles are somewhat larger and in the forebody extend farther median than 

 is shewn in Yamaguti's figure. Eggs are somewhat smaller, 48 to 54 by 26 

 to 30 IX as compared with 57 to 70 by 31 to 42 jx. Most details are in 

 agreement, e.g. the sucker ratio, the large pharynx, the length of the 

 esophagus, the position of the genital pore, the extent of the vitellaria, ex- 



