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



below. Outer lip thin ; in the sinus it is slightly thickened and very shortly reverted ; 

 in its course it forms a semicircular curve, a little contracted inwards in the middle, but 

 slightly patulous at the canal. It scarcely retreats in the slightest degree at the sinus, 

 which is round, open, shallow, and close to the body ; below it the lip-edge advances 

 with a considerable sweep to the edge of the base, from which point it curves backwards to 

 the canal ; there the edge is thin and patulous but not reverted. Inner lip is thinly 

 excavated in the substance of the shell, and is very narrow ; concave above, it advances 

 straight down the shortish, conical, small, but strong-pointed pillar, which has a narrow, 

 but blunt, and scarcely twisted edge. Operculum small, triangular, with a blunt terminal 

 apex ; it is pale straw-coloured, and is slightly corrugated with unequal furrows following 

 the lines of growth, some of which lines on the pillar-margin are slightly laminated. 

 H. 0-9 in. B. 0-36. Penultimate whorl, height 0-16. Mouth, height. 0'4, breadth 0'19. 



In general form this is like Pleurotoma studeriana, v. Mart., from Kerguelen ; but the breadth 

 of the whorls lies at a much higher point in each, the concave furrow below the suture is wanting 

 in that species, the ribs here are finer and sharper, more crowded and more oblique, and the apex is 

 smaller and more cylindrically prominent. Pleurotoma patagonica, v. Mart., is also similar ; but in 

 that the snout is much narrower and longer, the sinus is deeper and more remote from the suture ; the 

 ribs, which in form are similar, are shorter, much less oblique, and die out on the penultimate whorl ; 

 and the whole surface is much more strongly cancellated. In sculpture and form of sinus it is some- 

 what like Pleurotoma fuegensis, E. A. Sm. In the specimen from Station 149d, which I attribute to 

 a var. cariosa, the concave furrow below the suture is almost absent, and the aspect of the shell is 

 somewhat different; but both these features are perhaps a mere deception of the eye caused by the 

 rubbing down of the ribs, which are much wasted. 



50. Pleurotoma (Typhlomangelia) lithocolleta, 1 Watson (PI. XXIV. fig. 6). 



Pleurotoma {Typhlomangelia) lithocolleta, "Watson, Prelim. Report, pt. 9, Journ. Linn. Soc. Lond., 



voL xv. p. 441. 



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

 West Indies. 450 fathoms. Pteropod ooze. 



Shell. — High, narrow, conical, with a short base and a blunt apex, bluntly angulated 

 and tubercled, thin, smooth, ivory-white. Sculpture : Longitudinals — there are none but 

 very fine scratch-like lines of growth ; behind and parallel to the lip-edge there are three 

 narrow sickle-shaped ribs, which are probably an accidental feature. Spirals — very slightly 

 above the middle of the whorls runs a feeble angulation set with round but a little 

 narrowed and obliquely elongated knobs, of which there are about 12 on each whorl ; on 

 the first regular whorl there are about 10 ; before the end of the penultimate they have 



1 XikxoXKrjToc, gemmed. 



