PEOCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 81 



specimens it has a diameter of 430/j,, but in some small specimens the 

 diameter may be no more than half of this. The oral sucker is an- 

 terior in position, and measures from about 60/x to lOO^a in diameter. 

 The pharynx lies immediately behind the oral sucker, and slightly 

 more ventral in position. It is usually elongate in shape; in large 

 specimens it measures lOOju to 110/x in length by 60/a in width, while 

 in small contracted ones it may measure only about 60ja to TO/x in 

 each direction. The intestinal ceca fork very shortly behind the 

 pharynx and continue back at least to the region of the sex glands, 

 but their terminations could not be seen with certainty even in sec- 

 tioned specimens. The ventral sucker lies one-third, or a little lesb, 

 of the length of the body from the anterior end, and is often par- 

 tially concealed by the holdfast organ. It is somewhat larger than 



/ 'nir}. 



Figure 1. — Sketches of eight specimens of Proalaria rariabilis, new species, show- 

 ing variations in size, form of body, and tentacular or suclcing organs 



che oral sucker and is transversely elongated ; the measurements vary 

 from 97fji by 112/x to 60/x by 92/x. 



The testes, lying in the posterior portion of the body, vary a great 

 deal both in size and shape. Typically they lie one behind the other, 

 stretching transversely across the body, but in a number of specimens 

 they seem to lie either in a diagonal position or directly beside each 

 other. In a typical large specimen in which the testes lie one behind 

 the other, these organs measure about 450/x in width by about 200/i 

 in length. These measurements are, however, of little value, since 

 there is such an extreme variation in shape and size. The sperm duct 

 is enlarged to form a very stout and somewhat coiled tube, which 

 serves as a seminal vesicle. It usually occupies the posterior por- 

 tion of the body behind the testes. It opens into a genital atrium 

 on the dorsal side near the posterior end of the body. The ovary 



