Occasional Papers of the Museum of Zoology 33 



The radula of the living specimen agrees with this species, 

 although it is so juvenild that only 8 points occur on the 

 D-lateral. No Neritidae were found in the truly fresh water 

 habitats, and these were the only specimens (outside of the 

 genus Nerita) obtained from salt or brackish water, although 

 a number of promising localities were examined. 



HELICINIDAE 



Stoastomops walkeri H. Burrington Baker 

 (1924; Naut. XXXVII, 89) 



Type locality : (B4) valley on western slope of Montague, 

 Bonaire. 



Distribution: Bonaire, limestone hills (B3-8) ; Klein-Bonaire, 

 central portion (Kl). On the underside of surface rocks, 

 usually cemented so firmly into cavities and crevices that it is 

 very difficult to remove specimens entire. 



Shell (fig. viii-20) : depressed turbinate, subacuminate ; thin 

 and fragile. Color: golden brown to distinctly reddish, 

 "Whorls: 4i/^, markedly convex; suture well marked. Later 

 whorls: growth wrinkles pronounced but rather irregular; 

 spiral thread-riblets fine and numerous (about 30 on last 

 whorl), but irregularly spaced, more obscure on base of 

 shell. Embryonic shell : % whorls ; white ; practically smooth 

 but with irregular growth-wrinkles and punctations present. 

 Umbilicus : narrowly rimate. Aperture : subbasal, renif orm, 

 internally deep orange. Peristome : simple, sharp, incom- 

 plete; columellar wall deflected and thickened by whitish 

 callus, which spreads out extensively on base of penultimate 

 whorl but terminates abruptly, at its distal end, so as to 

 form a slight, but distinct emargination just above the basal 

 angle. 



Operculum (fig. viii-21) : horny plate whitish and very 

 thin, but slightly larger than the yellowish, calcareous one ; 

 the outer surface of the latter very slightly concave, with 

 minute, raised punctations; inner surface with eccentric 

 growth-lines and with subspiral nucleus at apex of rather 

 broad, parietal triangle. 



