The No7t-Marine MoUusca of Portuguese East Africa. 177 



ganglia lay above the anterior end of the buccal mass, considerably 

 in front of the oesophagus and buccal ganglia. The arrangement of the 

 ganglia comprised in the nerve-collar, and the relative lengths of the various 

 connectives and commissures, will be seen from fig. 3, and present no 

 unusual features. The otocysts are very prominent. 



Digestive system. — The jaw is 1-6 mm. in length, rather thin, and very 

 faintly transversely striated. 



The radula measures 3x1-2 mm. when flattened out. The central 

 teeth are very narrow, and each has an extremely short single cusp (PI. VII, 

 fig. 1). Both the lateral and marginal teeth are bicuspid, no endocones 

 being developed. The mesocones are large, with flanges on their inner 

 sides ; and those of the marginal teeth have somewhat rounded points. 

 The ectocones are uniformly small but quite separate from the mesocones. 

 The bases of the teeth are of the usual quadrate form. The transverse 

 rows curve very slightly forwards on each side of the middle line. The 

 radular formula is : (26+1 + 27) X 100. 



In another specimen the radula proved to be very similar, except that 

 there were fewer transverse rows of teeth, the formula being (27+1 + 27) X 77. 



The two salivary glands are united above the alimentary canal. 



Free retractor muscles. — The right and left divisions of the columellar 

 muscle are separate practically from their origin. The right portion divides 

 far forward into a broad ventral muscle to the foot, the so-called tail re- 

 tractor and two narrower dorsal muscles, the penial retractor and the right 

 tentacular retractor. The latter divides again into the retractor of the 

 lower right tentacle, which passes to the left of the penis, and the retractor 

 of the upper right tentacle, which passes between the penis and the vagina. 

 The left division of the columellar muscle gives rise to the buccal retractor 

 as well as to the left tentacular retractor. 



Reproductive organs (PL VII, fig. 5). — The hermaphrodite gland consists 

 of a rather small bunch of narrow follicles embedded in the posterior division 

 of the liver. The hermaphrodite duct is somewhat swollen and densely 

 convoluted throughout the greater part of its course. Close to its lower 

 end it takes a sharp bend, and at the angle of this bend there is a very 

 small swelling, which probably represents the vesicula seminalis. The 

 albumen gland is rather small, tapering, and peculiarly sacculated along 

 its sides. The common duct is large but not convoluted. The free oviduct 

 is short. The receptaculum seminis or spermatheca lies against the common 

 duct close to its anterior end. It is borne on a short receptacular duct 

 with an enlarged base, which forms a continuation of the long and broad, 

 thick-walled vagina. 



The vas deferens is very slender, and is slightly convoluted near the 

 vagina. It passes into a somewhat reniform structure, which leads into 



