1873.] F. Stoliczka — Land-shells of Penang Island. 13 



The jaw is smooth, semilunar, with a romid projection in the middle of 

 the concave edge ; it is about 2.5 m.m. broad. 



The radula is comparatively of very great length. In a middle-sized 

 specimen it measured 7 m.m. in length and 3 m.m. in breadth, although 

 one of the ends was not quite perfect. I counted 106 transverse rows 

 and about 141 teeth in each row. The centre tooth has a comparatively 

 short point without any lateral denticles, and is somewhat smaller tlian the 

 adjoining laterals. The first of these has a long, laterally bent, rather blunt 

 projection ; the following very gradually decrease in size and the middle 

 cusp becomes gradually more pointed and curved, while the basal plate 

 decreases. With about the fiftieth tooth the end begins to become bicus- 

 pid, and on about the hundreth tooth on either side, the two cusps are sharp- 

 est and best developed. 



Semper (lieisen im Archipel der Philipp., Vol. Ill, p. 68) says that 

 Mhysota does not possess any developed shell lobes of the mantle. In the 

 present species their existence is undeniable, and still all the other charac- 

 ters of the animal and shell point towards the greatest relation of R. cymatium 

 to other typical species of the genus, which scarcely would have any meaning, 

 if it were restricted in the sense given to it by Semper. I very much doubt, that 

 all the species with polished lower surface of the shell, referred by Semper to 

 Mliysota^ have no shell-lobes. How then do they produce the smoothness of the 

 shell ? I generally found shell-lobes essential for that purpose. But sup- 

 posing some of the species really had no shell-lobes, this would be no sufficient 

 reason for excluding any other species which possess them from Bhysota ; for 

 in JCesta we have a similar mixture of forms with and without shell-lobes. 



Thus the only anatomical difference, which remains to be considered as 

 distinguishing Mhysota from Xesta, is the simple form of the genital organs 

 in the former. How far this character is really reliable for generic distinctions, 

 is a point by no means easily settled, as I had already occasion to notice 

 when speaking of the anatomy of the two species of Sitala (Conulema, olim) 

 (Journ. A. S. B., Vol. xl, Pt. ii, 1871, p. 236 &c.), S. attegia and aS^. infula. 



When we compare the characters relating to the presence or absence 

 or form of the mantle lobes, we meet with a perfect similarity between 

 Wiysota and Rotula. The distinction between the two merely rests in 

 the presence of an amatorial gland in the latter genus, while the shells 

 only differ in the upper side of Bhysota being irregularly corrugated, and 

 in Rotula reticulately striated, or transversely costulated. 



In speaking of the sliell of Bhysota, Albers gives the peculiarly rugose 

 upper surface as one of the most important cliavacters of the genus. 



