60 Papers from the Marine Biological Laboratory at Tortugas. 



immediately behind pharynx, ventral, median; cirrus-pouch pyriform 

 with conspicuous prostate and muscular cirrus; seminal vesicle a con- 

 spicuous and convoluted tube lying to the left and behind the cirrus- 

 pouch; cirrus-pouch and seminal vesicle lying in neck. Testes 2, rather 

 small, somewhat pyriform, nearly opposite, and nearly at the middle 

 point of the length of the body. Ovary long-oval, near the posterior end 

 of the body, with the shell-gland at its caudal border; vitelline glands 2, 

 subglobular, behind the ovary and touching each other, the more anterior 

 one in contact with the ovary. A fold of the uterus lies behind the vitel- 

 line glands, and other folds fill the space not occupied by the other organs 

 between the ovary and the ventral sucker. A muscular seminal recep- 

 tacle, pyriform in shape and about the size of a testis, lies a short distance 

 behind the testes. The metraterm passes ventrad of the seminal vesicle 

 and cirrus-pouch and opens at the genital aperture. The ova are small 

 and very numerous. 



Dimensions of the specimen mounted in balsam: Length 1.47; 

 breadth, near anterior end 0.18, at ventral sucker 0.22, near posterior 

 end 0.35; length of neck 0.36; oral sucker, length 0.08, breadth 0.04; 

 pharynx 0.03 ; ventral sucker 0.18; ova 0.024 by 0.013. 



Host, Pomacanthus arcuatus: July 18, 1906, i fish examined, i dis- 

 tome. 



This distome was not studied much at the time of collecting. The 

 following measurements were made on the living worm: Length 1.82; 

 breadth, anterior 0.21, middle 0.32, posterior 0.35 ; oral sucker 0.09; ven- 

 tral sucker 0.22; ova 0.025 by 0.014. 



Hemiurus merus sp. nov. (Fig. 138.) 



The distomes which are referred to this species agree so closel}^ with 

 the species which I have recorded under the name Distomum appendicu- 

 latum (Bull. U. S. Fish Commission for 1899, p. 289, plate 36, figs. 25, 26) 

 that I was at first disposed to refer them to that species. When they are 

 compared with specimens in my collection from the alewife they are seen 

 to be specifically different. Although the character of the seminal ves- 

 icle in this species is different from that required for the genus Hemiurus, 

 I place it in that genus, preferring to extend the limits of the genus rather 

 than to be a party to any further dismemberment of the genus. 



The following description is based on specimens which were stained 

 and mounted in balsam. 



Body cylindrical to fusiform and clavate, crossed by stris which 

 make a sharply serrate outline, distinct on the margins as far back as the 

 ovary, dorsally not usually distinct so far back as the ventral sucker; 

 appendicular portion approximately equal to half the length of the body 

 proper; neck short, tapering, slightly arcuate. The rami of the intestine 

 enter the appendiculate portion when the latter is extended. In some 

 which have the appendix retracted the intestines appear to stop at the 

 anterior end of the appendix. Mouth ventral; ventral sucker about 

 twice the diameter of the oral sucker. Genital aperture at posterior 

 ventral border of oral sucker; cirrus smooth, cirrus-pouch rather slender, 

 reaching usually to about the middle of the dorsal side of the ventral 



