8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.60. 



are located between the two testes. A receptaculum seminis is 

 absent. The vitellaria are in the form of large acini extending 

 from a level posterior to the acetabulum to the second testis 

 or they may occupy the greater part of the substance of the 

 clinging plug. The uterus is short and contains only a few but large 

 eggs, which measure from 0.100 to 0.146 mm, long and 0.06 to 0.097 

 mm. wide. The vaginal opening is ventral to that of the male in 

 the posterior extremity of the body. A genital sinus may be present 

 or absent, but a bursa copulatrix is lacking. The excretory system 

 is in the form of a subcutaneous network of vessels and capillaries. 

 The excretory pore is ventral with respect to the genital opening. 



Parasitic in birds and carnivores. 



Type species. — Prohemistomwn spinulosum Odhner, 1913. 



Key to species of Prohemistotmun. 



I Clinging plug extensively developed and 

 dome-shaped, occupying at least two- 

 thirds of the body length ; acetabu- 

 lum in anterior third of body, hidden 

 in ventral view by clinging plug; 



ciiTus protrusible Prolieyyiistomum industrium 



Clinging plug small, oval in shape ; 

 acetabulum midway of body length ; 

 cirrus not protrusible 2 



2. Body not over 1.0 mm. in length; oval 



in shape Prohemistomum spinulosum 



Length, 0.90 to 1.75 mm. ; posterior ex- 

 tremity of body tapering into a cylin- 

 drical appendix Prohemistomum appendiculatum. 



Following are brief descriptions of the two previously known spe- 

 cies of ProkeTnistomu7n : 



PROHEMISTOMUM SPINULOSUM Odhner, 1913. 



Plate 4, fig. 5. 



SpecifG diagnosis. — ProJiemistovnivi: The body is broadly oval 

 in form ; length, 0.75 to 1.0 mm. ; maximum width, 0.45 to 0.65 mm. 

 The anterior two-thirds to four-fifths of the body length is flat- 

 tened with the margins rolled ventro-posteriorly, producing a spoon- 

 shaped cavity which contains the clinging plug. The posterior body 

 region is not sharply separated from the anterior. The body is thin- 

 nest anterior to the clinging plug, but posterior to this level the 

 thickness increases and near the posterior end of the body the pro- 

 portion of the width to the thickness is 4:3. The cuticle is covered 

 with fine scales except on the clinging plug, the posterior end of the 

 body and the dorsal surface posterior to the anterior testis. The 

 oral sucker, 0.07 to 0.085 mm. in diameter, is small and weakly 



