6 C. M. Majplestone : 



the various stages of it ; and also it is the species in which he 

 says he saw the oral aperture underneath the peristome, which 

 caused him to determine the name of the genus, for the reason 

 that he considered the slit itself when completed forms the 

 perlsto/iiial oritice, and as it is formed before the oral aperture, 

 he assumed it to be therefore the primary orifice and the oral 

 aperture the secondary one ; and the occurrence of the two 

 orifices caused him to name tl).e genus Bi-pora. It is important 

 to note that he makes no mention of the occurrence of the slit 

 in his descriptions of the other species dealt with in his paper. 

 With regard to these " slits " I must confess that my reasoning 

 depends a great deal upon what I may call negative evidence. 

 It is to be regretted that Mr. Whitelegge did not illustrate his 

 paper with figures, showing the various stages of development 

 of which he speaks ; so that it is extremely difficult to deal 

 satisfactorily with the subject, and these " slits '" must at pre- 

 sent remain an unsolved enigma. 



Another point of interest in connection with the Bipni-ae 

 is that up to the time of the publication of Mr. Whitelegge's 

 paper there was no record of any ooecia having been seen upon 

 any species of this genus. In his description of B. pliilippin^ 

 ensis he states that they are present in that species, and his 

 description of them is, " external, globose, smooth, with 'a 

 faint fimbriated stigma in front " ; but he gives no figure. 

 Many, if not all, of the specimens of this species which are upon 

 the slide lent to me by the Curator of the Australian Museum, 

 had ooecia upon them, and as I had not seen them before, I 

 made a drawing of a portion ^f one zoarium, which is here 

 reproduced (Fig. 2) as they have never before been figured. The 

 ooecia agree fairly with the description, but I could not see 

 upon them the " fimbriated stigma," though there was on some 

 of them an irregular line apparently marking the limit of a 

 layer of tissue or thickening in the walls of the ooecia. The 

 ooecia are on the upper surface of the zoaria, which is slightly 

 convex, and nciir the periphery. In order to obtain a view 

 of the ooecial openings which are situated at the base of the 

 ooecia, it was necessary to tilt the slide so as to expose the edge 

 of the zoarium to view. Scattered among the zooecia are some 

 of the " semi-lunar slits " spoken of above. I have drawn a 



