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



diverging margins : toward the lower part of the mouth the lip runs out in a pinion- 

 shaped projection, retreating thence to the point of the pillar. Inner lip thin and 

 narrow, little concave, with a loug sharp-edged truncation of the point of the pillar. 

 H. 0-18 in. B. 0-08. Penultimate whorl, height 0-03. Mouth, height 0-08, breadth 0'03. 



The only specimen of this beautiful little species is not full-grown. It is broader in form and 

 finer in the apex than Plcurotoma bolbodcs, Wats., or any other member of that group, among which 

 it most resembles perhaps Plcurotoma stirophora, Wats. Possibly in a more developed condition it 

 may in form approach more nearly to Plcurotoma fiuctuosa, Wats., from which its sculpture entirely 

 removes it. 



45. Pleurotoma (Beta) dyscrita, 1 Watson (PI. XXIII. fig. 8). 



Pleurotoma (Tliesbia) dyscrita, "Watson, Prelim. Report, pt. 9, Journ. Linn. Soc. Lond., voL xv. 



p. 448. 



Station 23. March 15, 1873. Lat. 18° 24' K, long. 63° 28' W. Off Sombrero 

 Island, West Indies. 450 fathoms. Pteropod ooze. 



Shell. — Thin, white, narrowly oblong or fusiform, with a longish, scarcely tumid 

 body-whorl, a shortish, conical, convexly whorled, small-pointed, shallow-sutured spire, 

 and a long conical base. Sculpture : Longitudinals — there are delicate thread-like curved 

 lines of growth, which are strongest near the top of the whorls. Spirals — the whole 

 surface is equably covered with fine, faintly raised, rounded threads ; they are slightly 

 fretted by the longitudinals ; between them are little rounded furrows of about twice 

 their breadth. Colour: the spiral threads are porcellanous, the furrows translucent 

 white, and the surface is a little glossy. Spire rather short, conical, but slightly concave, 

 with hardly any interruption in its profile-lines by the very slightly impressed suture 

 and the convexity of the whorls. Apex consists of 2^ rounded subcylindrical whorls rising 

 to a small rounded point, where the extreme tip hardly projects and is bent down on one 

 side ; it is smooth and glossy, but retains traces of a ruddy epidermis with minute spiral 

 threads. Whorls 6 in all, of regular but rapid increase, rather high and broad, convex, 

 but sloping, and not tumid ; the last is very long and full, though not tumid ; and there 

 is little contraction on the long conical base. Suture slightly impressed, rather oblique. 

 Mouth large, open, and oblong, pointed above, scarcely contracted below, but truncated 

 at the end of the broad open canal. Outer Up : very equably curved in both its planes ; 

 it has a somewhat high and prominent shoulder above, between which and the body- 

 whorl lies the rather deep, wide, rounded sinus. Inner lip : there is a thin glaze on the 

 body and on the long pillar, which is cut off in front with a long, thin, twisted, oblique 

 edge. H. 0'35 in. B. 0-16. Penultimate whorl, height 0"8. Mouth, height 0'22, 

 breadth 0-08 (?). 



1 SJaxoiroc, of difficult determination. 



