190 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 15 



large oval masses of the same dense and deeply staining, but histologically 

 indeterminable, tissue that underlies the spiny layer of the main part of 

 the cirrus sac. Fig. 7 gives a view of the three spines as made out from 

 parasagittal sections. 



Because of the fold already mentioned, presumably not natural, the 

 female gonopore is brought rather near the male gonopore. One may 

 suppose that naturally it would be well posterior to the latter. The 

 female gonopore leads into the excessively muscular terminal part of the 

 female canal, called the bulbous vagina by most authors but regarded 

 by me as a bulbous antrum. This has a very thick muscular wall of inter- 

 lacing, mostly circular fibers, and is lined by a heavily staining scalloped 

 layer that seems to be of the same nature as the material underlying the 

 spines of the cirrus sac. This material may be regarded as cuticularized ; 

 but in the female canal it does not bear any spines. The muscular wall 

 continues inward for some distance, gradually diminishing in thickness. 

 One may suppose that the vagina proper begins where the cuticularized 

 lining ceases. The vagina curves forward and pursues a long course 

 through the cement glands as a very narrow tube receiving these glands. 

 After reaching the level of the spiny part of the cirrus sac, the vagina 

 curves backward dorsal to itself and widens into a short section, lined by 

 a cuboidal epithelium, that does not receive any cement glands. This 

 soon terminates in a downward curve entered by the two oviducts. There 

 does not appear to be any Lang's vesicle, that is, any continuation of the 

 female canal beyond the entrance of the oviducts. 



Differential characters. — There are about fifteen valid described 

 species of Planocera. The present species differs from all of these in its 

 extremely broad shape. Even assuming that the animal is oval rather than 

 circular when fully extended, it is still definitely broader than any of the 

 other species. It is also among the larger species. The lining of the cirrus 

 with small spines is characteristic of the genus ; but the presence of large 

 teeth at the exit of the cirrus into the male antrum occurs in only a 

 few species. Apart from the finding by Kato (1938) of a large tooth at 

 the cirrus exit as an aberration in a specimen of P. pellucida, large teeth 

 around the cirrus tip are reported as specific characters only in P. armata 

 Laidlaw, 1902, P. crosslandi Laidlaw, 1903, and P. uncinate Palombi, 

 1939. In the last, there is a circle of spines of moderate size around the 

 cirrus tip, and other details of the copulatory apparatuses differ greatly 

 from those of the present species. In P. armata, the cirrus tip bears a 

 circle of six large spines and there is also a cuticularized ring at about 

 the middle of the cirrus sac. P. crosslandi, however, is armed with three 

 large hooks at the cirrus tip and therefore comes closer to tridentata than 



