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



and projects on the right side into a long, narrow, and very slightly twisted snout. 

 Suture a fine, sharp, deeply impressed line. Mouth club-shaped, being oval above, with 

 a sharpish angulation at the upper point, and being produced into a long, rather narrow, 

 but slightly widening canal, which is open in consequence of the oblique cutting away 

 of the pillar-lip. Outer Up, which is thin, sharp, and patulous, with a slight contraction 

 on the edge of the canal, leaves the body nearly at a right angle, and advances with a 

 very slight convexity to the keel, above which lies the deep, thin-lipped, U-shaped sinus, 

 whose lower margin lies parallel to, but a little above, the carinal thread ; from the keel 

 the lip has an edge which on the front is first convex and then very slightly receding, 

 while on the side it is first convex and then concave to the point of the snout, where its 

 course is very straight. Inner Up a thin, porcellanous glaze, spreads a little on the body, 

 from which the spirals are slightly cut away ; the lip is a little concave above, then 

 straight, and is early and obliquely cut away on the front of the pillar, where it is slightly 

 prominent, and finally it runs out to the point of the snout as a thin edge bordering the 

 canal. H. L47 in. B. 0'48. Penultimate whorl, height 0-24. Mouth, total height 0'8, 

 breadth 0-26. 



This species extremely resembles Pleurotoma staminea ; nor should I be at all surprised if, on a 

 fuller series of specimens being obtained, the two species should be ultimately united ; but the four 

 specimens of the former and the three of the present species obtained by the Challenger are constant 

 to one another and easily distinguishable. Besides distinctions which stand out in the description, 

 the form in Pleurotoma trilix is slimmer, as if the whorls were more closely twisted ; the snout is 

 longer, finer, a little twisted, and is striated to the point ; the shell is stronger, the pillar-edge of 

 the front canal where obliquely cut off is a little more contracted ; the suture is much more deeply 

 impressed, the apex is a very little larger, and very slightly more pressed down on one side. The 

 sculpture, too, is crisper, sharper, and smaller in the spirals, so as to produce a markedly different 

 texture. In Pleurotoma staminea, where an inferior keel faintly appears, it lies much lower than in 

 Pleurotoma trilix, in which it lies markedly above the suture. 



Like Pleurotoma staminea, this species is by the length of its canal excluded from the Spirotropis 

 group. 



17. Pleurotoma (Surcula) lepta, Watson (PL XVIII. fig. 7). 



Pleurotoma (Surcula) lepta, Watson, Prelim. Eeport, pt. 8, Journ. Linn. Soc. Lond., vol. xv. p. 391. 



Station 157. March 3, 1874. Lat. 53° 55' S., long. 108° 35' E. Southern Ocean, 

 south-west of Australia. 1950 fathoms. Diatom ooze. Bottom temperature 32 - l°. 



Shell. — High, fusiform, rather tumid, conical, with a produced base and a very long 

 fragile snout, thin, white, with very little sculpture. Sculpture : Longitudinals— the 

 whole surface is closely scored with fine striae in the lines of growth ; of these, at irre- 

 gular intervals of about y^j inch apart or rather more, one rises' into greater strength 

 and prominence as a rounded thread ; these are stronger and more regular on the earlier 



