POLYCLAD FLATWORMS — HYMAN 557 



The female gonopore, located shortly behind the male gonopore 

 and almost reached by the protruding cirrus papilla, leads into a 

 vertical female antrum from which the long vagina slants anteriorly, 

 paralleling the cirrus sac, then curves backwards and descends towards 

 the ventral body wall. The ascending part of the vagina is glandu- 

 lar, lined by a tall epithelium that receives the numerous cement 

 glands. Shortly after curving backward, the vagina alters into a 

 strongly muscular tube with a cuticularized lining. The thick mus- 

 cular wall of interwoven muscle fibers pursuing a mostly circular 

 course is well delimited from the surrounding mesenchyme. After 

 turning doAvnward, the vagina again alters its histological character, 

 losing the definite muscular coat and becoming lined with a tall 

 cellular epithelium. As it continues to descend, the vagina enlarges 

 into a sac that receives into its anterior wall the common oviduct; it 

 then narrows again as the duct of Lang's vesicle that makes an up- 

 ward bend and terminates in a small oval Lang's vesicle (fig. 5a). 

 A copulatory bursa is wanting. 



Differential diagnosis : Aquaplana pacifica differs from the only 

 other species of the genus, A. oceanica (Hyman) (1953b), in the lack 

 of a copulatory bursa and the much smaller size of Lang's vesicle. 



Holotype: USNM 28648, one whole mount with copulatory region 

 removed, the latter as sagittal sections (three slides). 



Remarks: There is good correspondence between the general and 

 copulatory anatomy of the two species of Aquaplana. In A. oceanica 

 the spermiducal bulbs and prostatic vesicle are not quite as closely 

 incorporated with the cirrus sac as in A. pacifica. In both species 

 the vagina is differentiated into glandular and muscular regions. 

 The want of a copulatory bursa in A. pacifica seems to indicate that 

 this structure is not as taxonomically important as previously sup- 

 posed. Its lack in A. pacifica would certainly not warrant separating 

 the latter into a distinct genus. The important character of the 

 genus appears to be the cirrus papilla armed with thorns. In A. 

 oceanica thorns are also present on the wall of the male antrum but 

 these are wanting in A. pacifica. 



Paraplanocera fritillata, new species 



Figures 5b-d; 6a 



Material: One specimen taken by Reish from rocks on the reef 

 flat at Eniwetok Atoll, Sta. E-123, Sept. 7, 1956. 



General characters: The specimen (fig. 56) is of broadly oval 

 form, measuring 19 by 17 mm., of thin, transparent texture, with 

 ruflSed margins. The color is yellowish gray, slightly mottled with 

 brown, and under magnification a cloud of black dots is seen over 



