OPEAS GRACILE. 129 



lete fold in the middle; rimation punctiform. Length 9, 

 diam. 2.5, aperture 2.5 mm. long" (Moerch, Journ. de 

 Conchyl. xx, 1872, p. 313). 



Nicobar Is. : Nancouri, one specimen under the bark of a 

 tree (Kjellerup). 



"Opeas apex of Java differs by its thicker epidermis, its 

 wider columella pnd less narrow umbilicus." A small form 

 found with the type is less narrow, the suture more strongly 

 crenulate in the middle, aperture shorter and rounded, not 

 narrowed, in front; length 8, diam. 1.5 to 2.66 mm. 



In Mauritius (pi. 23, fig. 23) the shells do not reach so 

 large a size as in Ceylon, etc., but are otherwise practically 

 typical. A series collected by Sir Charles Eliot at Takaungu, 

 on the coast of British East Africa in lat. 3 42' south (pi. 

 23, figs. 24, 25) also fall short of the maximum size, the two 

 figured measuring 10 x 3 and 8 x 2.6 mm., both with 7*4 

 whorls, the suture crenulate in the upper half of the shell's 

 length. 



New Caledonian form. The original description and fig- 

 ures of 0. souverbianum (pi. 24, fig. 31) and of 0. artense 

 (pi. 24, fig. 32) are given below. These seem to me to per- 

 tain to the more obese and more slender phases respectively 

 of one and the same species, which I am unable to distin- 

 guish from 0. gracile. E. L. Layard, of Noumea, the well- 

 known collector of New Caledonian shells, "maintained that 

 there was no difference between S. souverbiei, S. artensis, 

 8. tuckeri and the Ceylon species," the latter being 0. gracile 

 (P. Z. S. 1888, p. 358). The specimens before me from 

 Noumea, Art Island and He Casy, received from G. Dupuy 

 and E. Marie, support the reference to 0. gracile. They are 

 however a small form, not reaching the dimensions of typical 

 0. gracile. Shells from Noumea (pi. 24, figs. 40, 41, slender 

 phase) measure 8.8x2.8 and 8.8x2.2 mm., with 73,4 and 8 

 whorls. The stride are stronger below the somewhat crenu- 

 late suture, as usual. 



B. souverbianus Gassies. (PL 24, fig. 31). "Shell tur- 

 binate, elongate, not umbilicate, pellucid-buff, fragile, di- 

 aphanous, longitudinally delicately striate ; whorls 7, regularly 



