TOMLIN AND SHACKLEFORD : MARINE MOI.l.USCA OF S. THOME. 309 



ing very little and increasing very slowly in size, with heterostrophe, 

 yellowish apex, the last whorl being about twice the size of the 

 preceding and less than half that of the whole shell ; suture some- 

 what impressed ; aperture ovate, moderately acuminate above, about 

 two-fifths the length of the shell ; peristome acute ; columella 

 reflexed, almost straight with a strong plait on the lower part. 



Long.: 3'5 mm.; diam. max. i'5 mm. 



Hab. : S. Thome, not common, in coral gravel. 



This Odostomia, though very ordinary in appearance, we cannot 

 identify with any described species. 



It is akin to O. rissoides Hanley in size and generjil appearance, 

 but differs in being imperforate, less conical, less impressed at the 

 suture, and it has the plait or tooth lower down the columella. 

 Turbonilla ^pyrgidium sp. nov. (pi. 5, f 3). 



Shell small, narrow, very strongly turreted, longitudinally ribbed, 

 without spiral sculpture, white, shining, transparent, imperforate ; 

 whorls eight to nine, strongly keeled on the upper part near the 

 suture and flattened above the keel ; with smooth, heterostrophe 

 apex ; the longitudinal ribs, of which there appear to be about 

 twenty-four on the body whorl, are strongly marked on the upper 

 part of each whorl and form a series of beads where they cross 

 the keel, but on the lower part are evanescent ; columella arcuate, 

 without a visible plait ; aperture small, roundly oval. 



Long. : 3 mm. ; diam. max. '85 mm. 



Hab. : S. Thome, moderately common. 



This beautiful little shell, which is well represented by the 

 figure, is quite unlike any other species with which we are 

 acquainted. Owing to the filmy texture of the shell, it is extremely 

 difficult to count the number of ribs. 



All the type specimens are in the British Museum, 



Note on Turbonilla phrikalea Watson. — On plate 5, fig. i, of this number 

 I give a figure of a Turbonilla which is not uncommon in the S. Thome coral 

 gravel, and which I have no hesitation in identifying with the above species. 

 Watson described it (" Challenger'' Gasteropoda, p. 493) from a single worn broken 

 example, dredged at station 24, off Culebra Island. The colour, which he does not 

 mention, varies from dark to light fulvous brown. Watson spells the specific name 

 differently on the plate, but phrikalea is correct according to the derivation he gives. 

 — J. R. l.E B. ToMLiN {Read before the Society, March loth, 1915). 



TrrpytbtOl'^ liltle tower. 



