MANGELIA. 453 



of same in Macgilliv.* Moll. Aberd. p. 172, copied in 

 Brit. Marine Conch, p. 198, and Brown, Illust. Conch. 

 G. B. p. 127. 

 Pleurotoma leucosioma. Reeve, Conch. Icon. vol. i. Pleurot. pi. 31, f. 278. 



„ reticidatum, Macgilliv. Moll. Aberd. p. 173 (copied, Brit. Marine 



Conch, p. 199), probably. 



The general features of this shell present a striking 

 similarity to those of 31. turricula ; yet the points of dif- 

 ference are sufficiently obvious to ensure its discrimination. 

 It is of a narrow elliptic shape, and tapers nearly equally 

 from the middle to either extremity. It is tolerably, but 

 not very, strong, neither shining nor transparent, and of 

 an uniform milk-white hue. Its external surface is de- 

 cussated by spiral costellar lines, and very numerous nar- 

 row fold-like ribs ; the former, which are densely disposed, 

 and whicli for the most part (except towards the base of 

 the body- whorl) are broader than their intervening sulci, 

 are more or less flattened, and are chiefly conspicuous upon 

 the lower half of the final volution, where the folds, which 

 run from suture to suture down the turns of the spire, and 

 are never abruptly prominent, are no longer apparent ; 

 they frequently, too, become obsolete towards the outer 

 lip, or else become so fine as to form a kind of network 

 with the revolving lines. The spire, whose apex is de- 

 cidedly blunt, does not occupy more than two-fifths of 

 the total length, and is composed of five or six short and 

 slowly increasing turns, that are decidedly convex or 

 rounded, yet subscalar above. Their angulation, how- 

 ever, is not horizontally abrupt as in turricula, but rounded 

 off" and much more shelving ; upon the flattened area 

 above it the spiral lines, when visible at all, are finer, and 

 usually about three or four in number, and the ribs are 



* The description in Macgillivray (only derived, however, from two broken 

 examples) does not agree correctly with this species, but applies better to the 

 T. muricatus. 



