The Non-Marine Mollusca of Portuguese East Africa. 195 



lucent, while that in front and to the right of it is opaque and whitish in 

 alcohol. The receptaculum seminis or spermatheca is broadly oval and 

 nearly 2 mm. long, with very thin walls, and is borne on a short duct. 

 The vagina is rather short. 



The vas deferens runs forwards beside the oviduct, and is somewhat 

 convoluted in the posterior part of its course. It bears a nearly circular 

 compact prostate gland, which is situated between the glandular part of 

 the oviduct and the spermatheca, being slightly flattened by the pressure 

 of these organs. The vas deferens passes into the skin beside the female 

 opening, and emerges again into the body-cavity near the male opening, 

 whence it passes backwards to the penis. This organ is nearly three 

 times as broad as the slender vas deferens, and leads into the large penis- 

 sac, which is in turn three times as broad as the penis itself, both organs 

 being nearly 4 mm. in length. The penial retractor is inserted at the 

 junction of the penis and the penis-sac. The end of the penis next to the 

 vas deferens is somewhat swollen ; this is due to the fact that the terminal 

 part of the vas deferens is either contorted within the muscular penis- 

 sheath before opening into the penis itself, as shown in PI. VIII, fig. 11, or 

 else it is invaginated into the cavity of the penis to form a penis-papilla, 

 as shown in fig. 15. The epithelium lining the penis is furnished with 

 numerous small papillae. Inside the penis-sheath there are two longitudinal 

 folds, approximately opposite to each other, and numerous narrower 

 transverse or circular folds. The positions of the longitudinal folds, and to 

 some extent those of the transverse ones also, are shown by dark lines of 

 pigment on the outside of the penis-sheath. The anterior end of the penis 

 is often invaginated for some distance into the cavity of the penis-sheath. 



The spermatozoa (PI. VIII, fig. 10) have short, spirally twisted heads, 

 •0033 mm. in length, broad behind but sharply pointed in front. The tails 

 attain a length of more than -25 mm., and appear to be furnished throughout 

 almost their entire length with two narrow spiral flanges or ridges, which, 

 however, are most distinct close to the head, where one of them becomes 

 markedly broader, as shown in the figure. 



Subfamily PLANORBINAE. 

 Genus Planorbis Geofiroy, 1767. 

 Subgenus planorbula Haldemann, 1842. 

 Planorbis (Planorbula) pfeifferi Krs., 1848. 

 (Plate VIII, figs. 16-19.) 

 1848. Planorbis pfeifferi Krs., Sudafr. Moll., p. 83, pi. 5, fig. 7. D.F. 

 1899. Planorbis ruppelli, " Krs.," Junod, Bull. Soc. Vaudoise, xxxv, 

 D. 279. L. 



