Helminth Fauna of the Dry Tortugas. 51 



for a short distance toward the anterior end. The anterior end is prob- 

 ably broken. 



Dimensions: Length 1.40; breadth, anterior 0.42, middle 0.60; 

 maximum breadth about posterior fourth 0.72; ova 0.040 by 0.017. 



Distomum fenestratum Linton. (Figs, 105, 106.) 



These distomes were active, the neck, when fully extended, being 

 quite slender and as long as that part of the body which lay behind the 

 ventral sucker. When the neck was thus stretched out it was seen that 

 the convoluted tubule shown in sections (Proc. U. S. N. M., vol. xxxiii, 

 plate XIII, fig. 90) and in contorted specimen (Bull. U. S. Fish Commis- 

 sion, vol. xxxiv, plate xxx, figs. 213, 214) is really made up of the caudal 

 end of the esophagus and the beginnings of the intestinal rami. 



These specimens agree closely with the forms which I have described 

 from Coryphana at Beaufort and Lycodontis at Bermuda. Measure- 

 ments were not made at the time of collecting and the only specimen 

 which I have preserved is broken. The length, estimated, is 3.5 and the 

 breadth 0.40. Sections show the parenchyma to be reticulated. The 

 body-wall is lined with glands whose exact nature is not evident. They 

 strongly resemble the cells which I have interpreted as yolk-forming 

 cells in other distomes described in this paper. These cells begin on the 

 dorsal side in front of the ventral sucker. Behind the ventral sucker 

 they surround the body cavity to the posterior end. The diameter of 

 the oral sucker in the specimen sectioned is 0.08, of ventral sucker 0.19. 



Host, Hcemulon plumieri: 



1908, June 28, 2 fish, i distome; July 4, 12 fish, i distome. 



Host, H. sciurus: 



1907, July I, I fish, 2 distomes. 



Length of one in life 2.10, breadth 0.42. There was a rudiment of 

 a slender organ in front of the ventral sucker. 



XYSTRETRUM gen. nov. 



Etymology: rfWr//a, scraper, rasp; rjrptr/^ belly. 



Generic characters: Neck cylindrical; body suborbicular with a 

 thin border and thickened central portion, which is crossed on its ven- 

 tral surface by numerous, low, transverse ridges. Testes nearly opposite, 

 behind ventral sucker; ovary in front of testes; vitelline glands median be- 

 hind ventral sucker and in front of testes ; folds of uterus mainly behind 

 testes; genital aperture median, behind oral sucker; pharynx none. 



The posterior ends of the intestinal rami approximate, but whether 

 they actually unite could not be ascertained. 



Xystretrum solidum gen. et sp. nov. 



Distomum sp., Proc. U. S. Nat. Mus., vol. xxxvi, p. 119, plate xv, figs. 100-102. 



The most obvious difference between this and the following species 

 is the more compact character of the vitelline glands and the tendency 

 of the border to roll under in the Bermuda species. 



The longitudinal striae on the ventral disc are simply the longitudinal 

 muscle fibers of the body-wall. These striae are 0.02 mm. apart. 



