432 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



sac small, cylindrical to pyriform in shape; its tip can be projected as a 

 small genital papilla into a very shallow genital atrium (fig. 120). Male 

 duct and uterus entering sac separately, uniting near middle of sac to 

 form the short, tubular genital sinus (fig. 120). 



Ovary transversely extended, more or less median, about in middle 

 of hindbody. Seminal receptacle chiefly anterior to ovary. Three compact 

 vitellaria immediately posterior to ovary; anterior pair side by side, con- 

 nected by a narrow isthmus ; single, larger, bilobed posterior vitellarium 

 directly posterior to anterior pair and more or less median. Uterus coiling 

 backward some distance but not reaching posterior end of body; nearly 

 straight in region of acetabulum. Eggs thin shelled, elongate, 26 to 34 by 

 9 to 15 {X. Excretory pore ventral, a short distance in front of posterior 

 end of body; branches of vesicle unite dorsal to oral sucker. 



The name lissosomiim is from lisso (= smooth) and somum (= 

 body) and refers to the absence of the ventral papillae. 



Discussion. The genus Theletrum was named by Linton in 1910 for 

 a single specimen of a trematode collected from the black angelfish, 

 Pomacanthus arcuatiis, from Tortugas, Florida. A few specimens have 

 been collected there by the writer. The genus was named for the peculiar 

 cutaneous papillae posterior to the acetabulum. These are lacking in 

 T. lissosomum and are considered here as being a specific rather than a 

 generic character. T. lissosomum is fundamentally similar to T. fusti- 

 forme especially in the reproductive systems. Linton's description and 

 figure are incorrect in the so-called "cirrus sac," which is actually a typi- 

 cally hemiurid sinus sac. The 3 vitellaria and their arrangement are 

 probably prime generic characters, although in my Florida material these 

 vitellaria are sometimes so crowded together as to appear like one. 



The following generic diagnosis is proposed. 



GENERIC DIAGNOSIS OF THELETRUM LINTON, 1910 



Elongate, cylindrical hemiurids, without ecsoma; body smooth or 

 with ventral papillae, without denticulations, posterior end broadly 

 rounded or truncate. Acetabulum anterior to midbody. Intestinal ceca 

 extending to posterior end of body. Genital pore near intestinal bifurca- 

 tion Sinus sac cylindrical or pyriform; seminal vesicle tubular, preace- 

 tabular; testes diagonal, separated from one another and from the ovary 

 by the uterus. Ovary posttesticular ; seminal receptacle present ; vitellaria 

 postovarian, 3 in number, 2 side by side and one median and posterior. 



