NO. 2 HYMAN : POLYCLAD FLATWORMS FROM THE GALAPAGOS 193 



a definite lumen ; furthermore, the Lang's vesicle of this specimen is full 

 of sperm and hence is the true seminal receptacle. The coils of the sper- 

 miducal bulb of that side are seen in contact with the anterior end of the 

 bursa. Having received or given off the bursa stalk, the vagina bends 

 posteriorly, receives the common oviduct, and enters the Lang's vesicle. 

 Discussion. — As already mentioned, this species gave every indication 

 of belonging to Paraplanocera; but the presence of a long cirrus papilla 

 precludes inclusion in this genus. Only one other planocerid is known 

 that possesses a similar cirrus papilla, Planctoplanella atlantica Hyman, 

 1940; but in this the cirrus lacks an armature and the bursa is absent, 

 making it impossible to fit Aquaplana oceanica into this genus. In recent 

 years there have been attempts (e.g., by Marcus, 1947) to divide the 

 Planoceridae into two subfamilies, Planctoplaninae and Planocerinae. 

 The characteristics of Aquaplana oceanica throw grave doubt on the 

 validity of this distinction, since it has a long cirrus papilla as in the 

 Planctoplaninae, but otherwise closely resembles Paraplanocera, placed 

 in the Planocerinae. 



Family Prosthiostomidae 



Prosthiostomum parvicelis Hyman, 1939 

 Figs. 12, 13, and 14 



Material. — Three specimens were taken at station 187-34, Cartago 

 Bay, Albemarle Island, January 25, 1934, at 8 to 10 fathoms, on a 

 sand-rock bottom. The vial also contains a number of very young Iepto- 

 planids, not identifiable. 



Anatomical description. — This will be limited to points not brought 

 out in the original description. As the type specimen was broken in the 

 anterior margin, the marginal eyes could not be completely illustrated. 

 It is fortunate, therefore, that one of the specimens in the Hancock 

 collections is perfect in this region. The eyes of this individual are shown 

 in fig. 12. A second individual of what is presumably the same species is 

 young and immature, with fewer eyes, as shown in fig. 13. The third 

 specimen, like the type, has the male apparatus in a state of eversion. As 

 it seemed desirable to attempt to get sections of the everted apparatus, 

 this specimen was sectioned in a plane calculated to be parallel to the 

 everted apparatus. Although the sections were not quite longitudinal 

 with respect to the apparatus, they do show what was suspected in con- 

 nection with the type specimen, namely, that the entire male antrum 

 everts but the penis remains within the penis sheath. A somewhat re- 



