6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



Euplana (=Discoplana) is very similar to that of the genus Stylocho- 

 plana and in fact it is difficult to distinguish between these two genera. 

 The sole difference is that in Euplana there is no distinct prostatic 

 vesicle, whereas one exists in Stylochoplana. E. clippertoni certainly 

 resembles Stylochoplana in general external appearance, but has no 

 definite prostatic vesicle and hence seems to fit better into Euplana. It 

 differs from other known species of Euplana {•= Disco plana) in the 

 presence of a penis stylet. Euplana gracilis (Girard) is the most simpli- 

 fied member of the genus, having no penis papilla, stylet, or penis 

 sheath. 



Differential diagnosis. — Loosely arranged radiating cerebral eyes, 

 small penis papilla, penis pocket, penis sheath and short stylet present, 

 long muscular vagina with S-bend, small Lang's vesicle, genital pores 

 well separated. 



Locality. — Clipperton Island, under rocks to south of landing place. 

 Collected by Dr. Waldo L. Schmitt, July 21, 1938. 



Holotypc. — Whole mount with sex region removed ; set of sections 

 of sex region, U.S.N.M. no. 20425. Young specimen on same slide 

 with holotype. 



PROSTHIOSTOMUM PARVICELIS, n. sp. 



Figs. 13-15 



Description. — One specimen, 6 mm. long, of usual slender shape 

 typical of the genus, fully mature, bent in sexual region, part of an- 

 terior margin missing (fig. 14). Color not determinable. Eyes as 

 usual in the genus, comprising paired cerebral groups, and band of 

 eyes along anterior margin (fig. 13). Cerebral eyes consist of an 

 irregular curved row of 7 eyes on one side, 8 on the other, with a 

 single isolated eye lateral to the anterior end of the rows, on each side. 

 Marginal row of eyes unfortunately imperfect because of missing 

 anterior margin but obviously few in number compared to most other 

 species of the genus, of about 2 rows in central part of band, thin- 

 ning out around the sides to a few widely spaced eyes in a single row. 

 Pharynx typical of the genus (fig. 14). Because of bend in body mak- 

 ing good sagittal sections impossible, sexual apparatus was not sec- 

 tioned. Because of eversion of the male apparatus, most of this appa- 

 ratus can be seen in the whole mount. Male apparatus completely 

 everted as in copulation (result of fixation?) (fig. 15). Inside the 

 large cylindrical everted structure can be seen the oval seminal vesicle 

 with thick muscular wall and Indian-club shaped lumen, the 2 spheri- 

 cal thick-walled accessory vesicles (of unknown function), and the 



