552 THE VOYAGE OF H.M.S. CHALLENGER. 



16. Bittium delicatum, Watson (PI. XLI. fig. 5). 



Cerithium (Bittium) delicatum, Watson, Prelim. Report, pt. 5, Joum. Linn. Soc. Lond., vol. xv. p. 120, 



sp. 20. 



Station 135c. October 17, 1873. Nightingale Island, Tristan da Cunha Islands. 

 100 to 150 fathoms. 



Shell. — Small, narrow, conical, blunt, rather tumid on the base, ribbed but not reticu- 

 lated, thin, translucent, glossy, white, with slightly convex outlines. Sculpture : Longi- 

 tudinals — there are on each whorl about 17 narrow, straight, rather tumid ribs, parted bj- 

 furrows of about the same breadth. These ribs run straight down the spire, but are on 

 the body-whorl slightly oblicpie. This whole system of ribs and furrows ceases abruptly 

 at the edge of the base through a levelling up of the surface. There are many micro- 

 scopic rounded lines, which are most distinct in the furrows, but especially on the base. 

 Spirals — there are faint and minute spiral threads, best seen near the suture ; and there 

 are also indistinct close-set microscopic threads. The top of the pillar is encircled by a 

 minute sharp thread, which is the scar of the siphonal cut. Colour clear, translucent, and 

 glossy white. Spire high, narrow, with slightly convex outlines, which are strongly 

 impressed at the suture. Apex rather abrupt, blunt and rounded ; the extreme point 

 hardly rises above the general curve. Whorls 9, rounded, but a little flattened on the 

 sides, and constricted at the top and bottom of each; they are of slow and regular 

 increase ; the last is a little larger in proportion than the rest. The base is rounded and 

 a little tumid. Suture a minute line lying in a deep, open, and rounded depression. 

 Mouth bluntly pointed above, with a rather broad rounded opening for the canal at the 

 side of and behind the pillar. Outer lip rounded, slightly incurved above, patulous and 

 projecting on the base, slightly retreating towards the canal, the edge of which is straight 

 all round. Pillar rather short, but not stumpy, scarcely at all twisted, and very little 

 truncated, the end being very much rounded, though there is a slight point on the left 

 side. Inner lip : there is a very thin glaze on the body, which runs straight out on the 

 pillar with a thinnish, but distinct edge. H. 0-133 in. B. 0"04. Penultimate whorl, 

 height 0'02. Mouth, height 0-03, breadth 0'019. 



In many of its features this shell is like a minute Terebra, but the form of the whorls rather 

 suggests Bittium. Unfortunately the canal is slightly chipped. It is much smaller than Cerithi- 

 opsis costulata (Moller) ; the ribs, too, are much smaller, and the apex is more turbinate. Than 

 Cerithium naiadis, Woodward, 1 this species is much slimmer, and has not the well-marked 

 spirals. 



1 Dr Gwyn Jeffreys assures me this species of Woodward is really the same as the Cerithiopds costulata 

 (Mbllur). Not having opportunity now of comparing them, I state the fact on his authority. 



