278 TYIUMIDELLID^. 



O. ALBA, Jeffreys. 



Thin, smooth, subperforated, oblong-conoid ; whorls more or 

 less rounded, of more or less abrupt elevation ; spire scarcely, if 

 at all, longer than the body : suture peculiarly profound. Mouth 

 large, broadly rounded below, not very acutely contracted above : 

 outer lip arched ; reflection of the pillar lip very slight j fold 

 very retired. 



Plate XCVI. fig. 9. 

 Odosiomki alba, Jeffreys, Ann. Nat. Hist, new ser. vol. ii. p. 3.37. 



After fruitlessly endeavouring to ascertain the limits of 

 this species, baffled hy the scarcity of specimens, we have 

 been compelled to content ourselves with describing the 

 dozen or so of individuals, from which ^Ir. Jeffreys origi- 

 nally constituted his species. Whether a longer suite 

 might not even connect the shell with Rissoides (which the 

 young are very like), or dubia, we know not; the former 

 chiefly differs in being imperforate, the latter by its greater 

 solidity, stronger tooth, and the less broadly rounded base 

 of its aperture. Even the supposed Exmouth variety of 

 nitida approaches the species with a suspicious degree of 

 closeness. 



The shell appears to be of a more or less oblong-conoid 

 shape, and to taper above to a tolerably fine yet little 

 prominent apex. It is smooth, thin, snow-white, and 

 composed of six rather large volutions, that are divided by 

 an oblique simple yet very profound suture. Their longi- 

 tudinal increase is rapid, so that the penult turn is high, 

 and although they are not truly scalar (except, perhaps, 

 one or two of the earlier whorls), they swell out above 

 more or less abruptly from the suture, instead of shelving 

 gradually thence (as in dubia). They are more or less 



