NO. 2 HYMAN : POLYCLAD FLATWORMS FROM THE GALAPAGOS 191 



any other Planocera species. Unfortunately, no figures of crosslandi were 

 given. The description indicates that it is a small, oval species (22 by 16 

 mm) ; that the prostatic vesicle is enclosed within the same sheath as the 

 cirrus sac, whereas in tridentata there is a separating constriction; that 

 the duct from the seminal vesicle enters the prostatic duct, whereas it 

 remains separate in tridentata; and that the female canal continues be- 

 yond the entrance of the common oviduct as a long thread-like Lang's 

 vesicle, whereas this vesicle is wanting in tridentata. These details appear 

 sufficient to differentiate tridentata from crosslandi, apart from the great 

 distance between their localities. 



Genus AQUAPLANA, new genus 



Definition. — Planoceridae of oval form and thin consistency, with a 

 pair of nuchal tentacles; with spermiducal bulbs; true seminal vesicle 

 wanting ; prostatic vesicle free ; cirrus sac scantily armed with spines and 

 provided with a long papilla, also armed with spines ; female antrum not 

 bulbous ; with a large Lang's vesicle ; with a large muscular bursa extend- 

 ing forward from the vagina as in Paraplanocera. 



Type species. — Aquaplana oceanica. 



Aquaplana oceanica, new species 

 Figs. 8, 9, 10, and 11 



Material. — One specimen taken at station 66-33, Tagus Cove, Albe- 

 marle Island, February 9, 1933, on a sandy bottom, at 10 to 20 fathoms. 



Anatomical description. — The specimen is about 16 mm long, oval in 

 shape, and has folded margins. There is a pair of nuchal tentacles, each 

 with its base encircled by tentacular eyes. The cerebral eyes are repre- 

 sented by a pair of clusters in front of the tentacles, with a few scattered 

 eyes between the paired clusters (fig. 9). The color was not determin- 

 able. The pharynx appears as a very small oval organ in the body center, 

 but might have been lost on fixation, as is often the case in polyclads. The 

 copulatory apparatus appears some distance behind the pharynx ; from its 

 sides the uteri, filled with eggs, extend forward to the tentacles. The 

 copulatory apparatuses as seen in the entire worm are shown in fig. 8. 

 There is indicated a free prostatic vesicle, entered at its attached end by 

 the two sperm ducts, without the formation of a seminal vesicle ; a cirrus 

 sac; a large Lang's vesicle; and a copulatory bursa extending anteriorly 

 alongside the male apparatus. These characters suggest at once Paraplan- 

 ocera, but sections show that the worm cannot be fitted into this genus. 



