SYKES — LAND AND FEESHWATEE MOLLUSCA. 



61 



12. Streptaxis {Imperturbatla) braueri. Martens. 



Streptaxis [Imperlurbatia] braueri, Martens, Mt. Zool. Mus. Berl. i. (1898) p. 13. 

 Mahe : Trois Fr^res, 1500 feet ; Mountain Forest, Cascade, 2000 feet ; Mt. x^lphonse. 

 Cascade, 1800 feet ; Morne, 2500 feet. 



13. Friodincus serratus, H. Adams. 



Disais serratus, H. Adams, Proc. Zool. Soc. 1868, p. 290. 

 Priodiscu.i serratus, H. Ad.; Martens, /. c. p. 14. 



Mah6: Cascade Forest, 1000 and 2000 feet; Mt. Alphonse, Cascade, 1800 feet; 

 Mt. Sebert, 1800 feet. 



Prasliu : Valley of Coco de Mer. 



14. Priodiscus (?) martensi, sp. n. (See fig. 3.) 



Shell depressed, trochiform, the outline being rather concave than convex, brownish 

 corneous, deeply, somewhat openly, umbilicated, the umbilicus being pervious to the 

 apex ; protoconch smooth, the next whorl is marked by coarse radiating riblcts, which 

 then cease and the residue of the shell bears only well-marked lines of growth ; peri- 

 ostracutn olivaceous, thicker at the sutures, where traces of prolongations may be seen, 

 periphery keeled and rugose ; whorls 5, regularly increasing, plano-convex, with fairly deep 

 sutures ; base flattened and angulated round the umbilical area ; mouth subquadrate. 



Alt. 2"75 ; diam. max. 6 millim. 



Silhouette. 



Fig. 3. 



Priodiscus (?) martensi, X 3. 



Two specimens only of a difficult form. At first sight the shell recalls the genus 

 Thysanota, but I have seen no species of that group with a similar sculpture on the early 

 whorls. From an examination of this sculpture compared with that of Priodiscus 

 serratus, Adams, combined with the fact that two young shells fell out of the mouth 

 of the type, I am led to place it here. P. serratus may be readily separated by its well- 

 marked sculpture over the whole of the shell. 



