RIEBECKIA. 205 



Radula of R. sokotorana, according to data supplied v. 

 Martens by Schako, has the middle tooth weakly tricuspid, 

 not so small as the simple one of Achatina. The lateral teeth 

 are bicuspid as in Limicolaria and Pseudoglessula retifera, 

 while they are tricuspid in most Stenogyras. The marginal 

 teeth are bicuspid as in Achatina, in part with the side cusp 

 bind. 



Type R. sokotorana. 



Distribution, Island of Socotra. 



Beyond the dentition, nothing is known of the soft ana- 

 tomy of this group. Its position in the series is therefore 

 quite uncertain. The species are figured on plate 54 and 

 part of 55. 



1. R. SOKOTORANA (Martens). PI. 54, figs. 73 to 79. 



Shell turrited, solid, delicately cancellated with vertical 

 wrinkles and impressed spiral lines, pale yellow and white, 

 uniform. Whorls 11-13, the first two forming an obtuse apex, 

 the following regularly increasing, a little convex, the later 

 whorls proportionally high. Aperture occupying about two- 

 aevenths the total length; outer margin simple, obtuse, 

 columellar margin arcuate, subvertical, obliquely truncate and 

 emarginate below. Length 56-76, diam. 18-24, length of aper- 

 ture 17-22, width 10-14 mm. (Marts.). 



Socotra: Eastern end of the island, on limestone. Occurs 

 in enormous numbers in the ground under rock ledges. 



. Achatina sokotorana v. MARTENS, Nach. mal. Ges. xiii, Oct. 

 1881, p. 135. Stenogyra (Riebeckia) sokotorana v. MARTS., 

 Conchol. Mittheil. ii, p. 147, pi. 29, f. 1-8 (1883). E. A. 

 SMITH, Nat. Hist. Sokotra etc., p. 131 pi. 13, f. 15, a young 

 shell. R. sokotorana KOBELT, Conch. Cab. p. 84, pi. 28, f. 1-3. 

 Stenogyra fumificatus GODWIN-AUSTEN, P. Z. S. 1881, p. 

 810, pi. 69, f. 2 (reproduced in SMITH, N. H. Sokotra, p. 131, 

 f. a, b.). 



The shells of this species are often used for pipe bowls by 

 the natives. It differs from the following species by the 

 large size of the apex, and the distinctly channeled suture, 

 especially of the upper whorls (pi. 54, figs. 77-79). 



