TREMATODES FROM FISHES — LINTON 51 



In older worms the anterior surface of the body is covered with 

 spines, but in younger specimens the surface is nearly devoid of 

 spines. The ventral sucker is a little larger than the oral, and the 

 pharynx is longer than the oral sucker. 



Measurements in formalin : Length, 7.8 mm. ; breadth of expanded 

 portion of the neck, exclusive of spines, 0.57 mm., in front of ventral 

 sucker, 0.21 mm., at middle of length, 0.29 mm., near posterior end, 

 0.35 mm. ; oral sucker, length, 0.11 mm., breadth, 0.15 mm. ; diameter 

 of ventral sucker, 0.19 mm.; distance from anterior end of ventral 

 sucker about 0.9 mm. 



In another specimen: Oral sucker, length, 0.11 mm., breadth, 0.15 

 mm. ; pharynx, length, 0.15 mm., breadth, 0.12 mm. ; ventral sucker, 

 length, 0.16 mm., breadth, 0,18 mm. ; ova about 0.042 by 0.024 mm. in 

 balsam. 



In the older specimens the ova fill the space between the testes, 

 which are at the posterior end of the body, and the seminal vesicle. 

 The cirrus is long and spinous, the cirrus pouch extending far back 

 of the ventral sucker, with the seminal vesicle at its posterior end. 

 The metraterm lies beside the cirrus pouch and is lined with spines. 



On July 20, 1924. two of these distomes, 4 and 6 mm. in length, 

 were collected from a small sturgeon measuring 85 cm. in length 

 (U.S.N.M. No. 8198). 



Genus STEPHANOSTOMUM Looss, 1899 



STEPHANOSTOMUM DENTATUM (Linton) 

 Plate 3, Figuke 25 



Distotnum dentatum Linton, Bull. U. S. Fish Comm. for 1899, pp. 283, 294, figs. 

 64-67, 1900 ; ibid., p. 483, 1901 ; Bull. U. S. Bur. Fish., vol. 31, pt. 2, p. 582, 

 1913. 



This species is smaller and relatively broader than S. tenuis; also 

 the ova are smaller, and the pharynx is relatively smaller. 



In strongly contracted specimens the pharynx is contiguous with 

 the oral sucker, but in individuals with the neck not greatly con- 

 tracted a prepharynx can be seen. There does not appear to be an 

 esophagus. The number of oral spines is 54; length of oral spines 

 about 0.05 mm. The entire body may be covered with closely placed 

 spines, most abundant on the neck, less numerous toward the poste- 

 rior end. Specimens were seen which had lost some of or all the 

 oral spines and most of the spines from the body. The body spines, 

 seen in front view, are somewhat scalelike with bluntly rounded 

 ends ; in edge view, as seen on the margins of the neck, they are slen- 

 der, tapering, and slightly recurved. The oral spines are of nearly 

 uniform diameter for the basal half of the length, then taper gradu- 



