POLYCLAD FLATWORMS — HYMAN 581 



from 5 to 30 in dijfferent individuals. As only one sexual specimen 

 of Nymphozoon bayeri is available it cannot be stated whether the 

 number of female apparatuses shows individual vai'iation. The lack 

 of a sucker is unusual but not unique in Cotylea. A sucker is absent 

 from Amakusaplana ohshimai Kato (1938a), and this author men- 

 tions two other cotyleans reported as devoid of a sucker; but it must 

 be admitted that the sucker is very often difficult to see in preserved 

 specimens. 



The color pattern of the present species somewhat resembles that 

 of Pseudoceros gratus Kato (1937), reported as common off the Palau 

 Islands (Kato, 1943) but not recovered in the present material. 

 Kato's species differs from Nymphozoon bayeri in that the margin has 

 a mere black line rather than a band, in the much narrower lateral 

 black stripes, and in attaining sexual maturity at a length of 50 mm. 

 Kato makes no statement about the sucker but declares there is a pair 

 of male copulatory apparatuses. The female apparatus is not men- 

 tioned. As already indicated, it appears to me that Pseudoceros 

 gratus is identical with Eurylepta striata Schmarda (1859) rather 

 than, as supposed by Kato, with " Stylochoplana" meleagrina Kelaart 

 (1858), in which the stripes are purplish and the tentacles are "occip- 

 ital," meaning, no doubt, nuchal. 



Genus Acanthosoon Collingwood, 1876 



Definition: Pseudoceridae with dorsal surface covered with small 

 papillae or tubercles; otherwise as in Thysanozoon. 

 Type species: Acanthozoon armatus (Kelaart) (1858). 



Acanthozoon nigropapillosus, new species 



Figure 13 



Material: One specimen found swimming off the reef edge at 

 Falarik Islet, Ifaluk Atoll, Sta. 616, collected by Migel, a native of 

 Sonsorol, Oct. 18, 1953, under the auspices of the Pacific Science 

 Board Atoll Research Program. 



GexVeral characters: The worm is of broadly oval shape (fig. 13), 

 measuring 15 by 14 mm., preserved. It is black with a pale yellowish 

 border, present in only a few places as the margin is damaged. The 

 dorsal surface is covered with low rounded black papillae tipped with 

 white, hence to the naked eye the dorsal surface appears black dotted 

 with white. This appearance is depicted in a small area on figure 13. 

 At the middle of the anterior end the tentacular folds are evident but 

 eyes could not be seen because of the black color. Behind the tentacles 

 an oval area houses the ruffled pharynx of which only a few folds were 

 detectable. The mouth opening, posterior to the pharynx middle. 



