^6 ADDITIONS TO THE TASMANIA MOLLUSCAN FAUNA. 



RISELLO'PSIS MUTABILIS (May), Figs, i and 2.— 

 Shell depressed of three whorls, rapidly increasing, 

 iimbilicate ; aperture large, descending in front, 

 angular above ; suture somewhat canaliculate. Two 

 prominent keels divide the shell into a superior, a 

 peripheral, and basal area. The lower keel is con- 

 siderably the stronger. There is a low ridge on 

 the base of the shell, and beyond it a small, sharp 

 keel, 'exactly defining the umbilical area, which 

 latter is whitish, whilst the rest of the shell is a dull 

 purplish black. Lip sharp and simple, somewhat 

 angled by the persistence of the peripheral keels, 

 which, however, have become nearly obsolete. 

 Columella arched, and slightly expanded over the 

 umbilicus, which is ample and perspective. Shell 

 almost smooth (often corroded), but very finely 

 striated by lines of growth. Height, 25^ ; greatest 

 diameter, 3^ mill. Habitat. — Most of my speci- 

 mens, including the type, are from Fred. Henry 

 Bay, Tasmania. It occurs in Victoria also (C. 

 Gabriel, F. H. Baker). 



Individuals may vary, by the keels — especially the 

 upper one — becoming almost obsolete, giving the 

 whorls a more rounded appearance. One example is 

 highly turretted, giving it a trochiform appearance. 

 Another has the last whorl partly detached. The colour 

 may also become reddish, mottled with white, or there 

 may be yellowish patches on a black ground. From the 

 N-ew Zealand species (R. varia), it differs in being less 

 round and without the keels on the base and upper part 

 of the whorl, and in wanting the coarse striation. Type 

 to be placed in the Tasmanian Museum, Figs, i and 2. 



The following note on the Genus Litorina was com- 

 municated by n^y friend, Charles Hedley, of the Austra- 

 lian Museum, Sydney, whom I also have to thank for 

 kind assistance in the preparation of this paper. 



"' LITORINA (Menke), 1828, non Littorina Ferussac 

 1822), nomen nudum. Ferussac (Tabl. Syst. des 

 Anim. Moll., 1822, p. xxxiv.), casually wrote Litto- 



NOTE. — This species was wmngly figured in Tate and 

 May's Census, PI. xxiii., fig. 9, as Fossarina Fmiiculata Teni- 

 son-Woods. 



