16 PROCEEDINGS OF THE NATIONAL MUSEUM vol.88 



sucker to the posterior end, where the lateral masses meet behind the 

 testis. There is a vitelline reservoir on the median line in front of 

 the level of the ovary. It is somewhat variable in shape and position, 

 depending on the quantity of yolk. What was interpreted to be a 

 seminal receptacle was seen in a few cases in front of the ovary. 

 The shell gland and ootype are about on the median line on a level 

 with the anterior portion of the ovary. The ova are elongate, with 

 a filament at each end. 



Measurements in balsam: Length, 2 mm.; breadth, at level of 

 anterior suckers, 0.07 mm., in front of sucker-bearing portion, about 

 0.75 mm.; diameter of anterior sucker, 0.027 mm.; pharynx, length 

 0.045 mm., breadth, 0.027 mm. ; ova diameter, 0.06 mm, ; length, exclu- 

 sive of filaments, about 0.26 mm. 



Hosts. — Alewife {Pomolobus yseudoharengus) and hickory shad 

 {P. mediocifis). 



Record of collections. — Five (U.S.N.M. No. 8159), collected August 

 11, 1908, from gills of alewife. Rami of intestines of most of them 

 bright red; numerous minute black pigment spots in lateral areas. 

 These worms were very active, contracting to a length of 0.6 mm. and 

 stretching to a length of 1.8 mm.; posterior suckers, four on each 

 side on very flexible and contractile pedicels, extending to more than 

 half the breadth of the posterior half of the body, and contracting 

 until no pedicel could be seen, the sucker even becoming immersed 

 in tlie substance of the body; six slender hooks at the posterior end 

 of the body, the part where they are implanted being very contractile, 

 the hooks being so arranged as to have a grasping motion; worms 

 fragile. 



Number not recorded, collected July 8, 1910, on gills of alewife. 

 Color by reflected light white, with numerous small brown pigment 

 granules; margins and anterior end translucent, by transmitted light 

 the axial region also translucent and somewhat yellowish. In a 

 few cases the intestines were red. Body crossed by fine, crinkly lines 

 with short, twiglike branchings. 



Many, collected on August 17, 1910, on gills of a 22-cm. alewife. 

 This worm has extraordinary powers of extension and contraction, 

 especially of the part anterior to the sucker-bearing portion. The 

 anterior end may be extended into a fine, threadlike neck, or it may 

 be contracted so that the whole worm is as broad as it is loner. These 

 changes take place very rapidly. 



One, collected August 20, 1910, from gills of hickory shad. 



One, collected July 6, 1912. After this date no special search was 

 made for gill parasites, since about this time the study of the mono- 

 genetic trematodes was taken up by Dr. MacCallum. 



