1903.] FROM ZANZIBAR AND BRITISH EAST AFRICA. 105 



the two vasa deferentia at its hinder end. Its walls are thin and 

 consist of circular muscle-fibres. 



The resemblance existing between these organs of Disparoplana 

 and those of Planocera and Paraplanocera is so great, that we are 

 compelled to assume a close relationship between these genera. 

 In the shape of the penis Bisparoplana approaches rather the 

 latter genus, whilst in possessing a single vesicula seminalis it 

 approximates rather to the former. 



Female apjjaratus. — The antrum femininum is large and rather 

 elongated. ■ The vagina, after running forward to receive the 

 separate openings of the uteri, is continued back as the accessory 

 vesicle which ends blindly after making a second turn forwards, 

 ventral to the fii-st pai-t of its course. The shell-glands open into 

 the accessory vesicle. 



The inclusion of this species in the Planoceridae will necessitate 

 an altei-ation of the definition of that family. I do not attempt 

 to offei- a new definitioii in the present paper, since it is necessary 

 to have information concerning the anatomy of a large number of 

 species the internal structure of which but little is known, before 

 any useful modification of Lang's definition can be suggested. 



However, it is permissible to point out here that the discovery 

 of such a form as Disparoplana indicates, I think forcibly, not 

 only that in the futui-e our definition of the Planoceridse will have 

 to be altered, but also that the Leptoplanida? may be a polyphyletic 

 family. 



The genus Disparoplana may be defined as follows : — An 

 elongated form, not provided with tentacles ; the eyes arranged 

 in two lines over the brain. Mouth a little in front of the middle 

 of the body. Penis cylindrical, armed with chitinous spines 

 resembling those of Planocera ; a well- developed prostate and 

 single large vesicula seminalis present. Female ducts simple, a 

 small accessory vesicle present. 



Stylochus zanzibaricus, sp. nov. 



Labelled " s.s. Juba." 



A small, rather elongate form. 



Length 10 mm. 



Breadth 4 „ 



Tentacles from anterior end 2*5 „ 



"Mouth" „ „ 7 „ 



Genital openings from hinder end ... '5 ,, 



No note as to colour, but to judge from the single spirit- 

 specimen, this is mottled reddish-brown and yellow on the dorsal 

 surface ; the ventral surface is uniform greyish yellow. 



The eye-spots are found on and about the base of the tentacles 

 a,nd on the anteiior margin, where they are of moderate size 

 (see text-fig. 5, p. 106). 



I have not found any definite group of brain-eyes. 



