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PROCEEDINGS OF THE NATIONAL MUSEUM 



Figure 16. — a, Acerotisa rugosa, copulatory apparatus as seen from above in whole mount. 

 b, c, Prosthiostomum exiguum: b, entire animal; c, eyes enlarged; d, P. griseum, anterior 

 end enlarged. (Explanation on page 597.) 



specimens measuring 4 mm. and 5 mm. in length (fig. 166). The 

 species is of the usual slender shape, broader anteriorly with rounded 

 anterior margin, tapering behind the pharynx to a blunt posterior end. 

 The color appeared to be a dirty white. The eye arrangement is shown 

 in figure 166, and enlarged in 16c. Along the anterior margin is a 



