NO. 14 manter: digenetic trematodes of fishes 381 



The name gastrocotylus is from gastro (= ventral) and cotyle (= 

 cup), and refers to the cuplike formation of the ventral body fold. 



Comparisons. P. gastrocotylus differs from all other species in the ge- 

 nus in the circular body fold enclosing the region near the acetabulum. 

 The median genital pore is not common in the genus. The fusiform shape 

 and the diagonal testes occur also in P. branchiostegi Yamaguti, 1937, P. 

 alacris (Looss), and P. crassigula (Linton). The two former species dif- 

 fer from P. gastrocotylus in position of genital pore, length of esophagus, 

 and smaller size, as well as in other minor characters. P. gastrocotylus is 

 without doubt most similar to P. crassigula collected from related hosts at 

 Tortugas, Florida. Specimens of P. crassigula collected by the writer 

 show the acetabulum somewhat sunk in the body and a muscular develop- 

 ment of the peripheral region of the body wall suggesting the body fold 

 of P. gastrocotylus. Both species have large pharynges and a very short 

 or no esophagus. P. gastrocotylus is somewhat wider and more fusiform. 

 Although Linton states that the genital pore of P. crassigula is near the 

 acetabulum, in my specimens it may be as far forward as the base of the 

 pharynx, thus corresponding to its possible position in P. gastrocotylus. 

 It is, however, slightly more to the left in P. crassigula. The two species 

 are enough alike so that they were thought for some time to represent the 

 same species. They seem to form an example of a pair of "twin species." 



Hamacreadium mutablle Linton, 1910 

 (Plate 40, fig. 64) 



Hosts: Lutianus viridis (Val.) 



Mycteroperca xenarcha Jordan (?) 



Location: Intestine 



Locality: Charles and Albemarle islands, Galapagos 



Number: 3 from one Lutianus, 6 from Mycteroperca (?) 



These specimens agree with H. mutabile Linton when the common 

 but rather marked variations occurring within this species are considered. 

 H. mutabile has been collected many times by the author at Tortugas, 

 Florida, where it occurs in Lutianus and related hosts. The extent of the 

 vitellaria is fairly constant. The follicles are confluent at the level of the 

 intestinal bifurcation, especially dorsally, and extend approximately to 

 mid-esophagus level. The lobing of the testes is highly variable and in a 

 single collection of specimens may vary through all degrees from smooth 

 to deeply lobed. The position of the genital pore is also variable. Usually 



