RISSOA. 107 



of certain specimens of tlie rufilahrwm and those of the 

 costata of Desmarest. The violacea again is a close ally. 



This solid Blssoa ranges in shape from ovate-conic to 

 oval conic, is scarcely translucent, has a resinous gloss, and 

 varies in tint from whitish horn-colour to dirty violet or 

 purple : when adult the hue is generally uniform, or the 

 pale ground is broadly and obscurely zoned with the darker 

 shade ; but in younger shells the whorls are traversed 

 lengthways by rather distant linear streaks of fulvous or 

 yellowish brown, which almost invariably disappear upon 

 the formation of the longitudinal ribs. These last when 

 present at all (which, however, is usually the case in the 

 fully matured individuals) do not extend to the base of the 

 body, but merely reach about half way down, are most 

 conspicuous upon the penult turn, occasionally run up the 

 antepenult, but rarely if ever appear on any of the smaller 

 turns. These ribs are strong, closely disposed, and more 

 frequently oblique than otherwise ; their interstices are 

 narrow and spirally striated with obsoletely raised lines, 

 the intervals of whose crowded decussation by still more 

 obscurely elevated longitudinal wrinkles upon the ribless 

 dorsal surface of the final whorl, cause the shell to appear 

 punctured in regular (not quincuncial) rows. The volu- 

 tions, whose longitudinal increase is moderately quick, are 

 divided by a simple fine and oblique suture, and (except 

 the last two) are rather short and somewhat flattened ; of 

 the six or seven, which compose the spire, and rapidly slope 

 to a rather fine point, the smaller or upper ones are per- 

 fectly smooth. The basal declination of the body, which 

 occupies one half of the entire dorsal length, and in the more 

 typical examples is about as broad as it is long, is gradual, 

 and not much rounded ; upon the ventral side, indeed, it 

 is rather flattened. The mouth, whose proportion to the 



