188 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 15 



Family Planoceridae 



Genus PLANOGERA de Blainville, 1828 



Definition. — Planoceridae of broadly oval to circular form, with 

 tentacular eyes encircling the tentacle bases; with true seminal vesicle; 

 prostatic vesicle free; cirrus sac large and muscular, with lumen lined 

 with small spines; with or without one to several large spines or hooks 

 at the exit of the cirrus sac into the male antrum; female antrum (vagina 

 bulbosa) heavily muscularized ; Lang's vesicle reduced to a small sac, its 

 duct often very long. 



Type species. — Planocera pellucida (Mertens) 1832. 



Planocera tridentata, new species 

 Figs. 5, 6, and 7 



Material. — One specimen of this splendid species was taken at station 

 30-33, Gardner Bay, Hood Island, January 26, 1933, on a rocky shore. 



Anatomical description. — This is a rather large species, of circular 

 form, 42 mm in diameter (fig. 5). It should be mentioned, however, that 

 there is a fold in the genital region, between the male and female gono- 

 pores; and if this were straightened out, the animal would probably be 

 slightly longer than wide. But in any case, the species is a very broad one. 

 The margins are frilly. The color is indeterminable but the species ap- 

 pears thin and transparent. There are the usual two nuchal tentacles 

 characteristic of the family. The tentacular eyes appear to be situated at 

 the base of the tentacles. The cerebral eyes form elongated groups over 

 the brain region. The pharynx (fig. 5) is about central, short and wide, 

 with a few broad lateral folds. The uteri, full of eggs, are seen on either 

 side of the pharynx, but do not meet anterior to the latter. The copu- 

 latory apparatus is seen in the whole specimen immediately behind the 

 pharynx, and shows the prostatic vesicle attached to the anterior end of 

 the cirrus sac ; but the posterior part of the latter is concealed by the mass 

 of cement glands that is pushed forward over it by the fold already 

 mentioned. This is unfortunate, for it would have been helpful to have 

 seen the armature of the cirrus sac, especially the three large teeth, in the 

 whole specimen. Their presence was not suspected until sections were 

 prepared. 



The copulatory region was removed and sectioned sagitally. Because 

 of the many teeth in the cirrus sac and the mass of cement glands, there 

 is a good deal of tearing in the sexual region ; but all points could be 



