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



20. Pleurotorna (Surcula) plebeia, Watson (PI. XXV. fig. 2). 



Pleurotoma {Surcula) plebeia, Watson, Prelim. Eeport, pt. 8, Journ. Linn. Soc. Lond., vol. xv. p. 395. 



Station 122. September 10, 1873. Lat. 9° 5' S., long. 34° 50' W. Off Pernambuco. 

 350 fatboms. Red mud. 



Shell. — Higb, narrow, fusiform, subscalar, angulated and tubercled on tbe angle, strong, 

 rough, yellowisb white. Sculpture : Longitudinals — tbe upper wborls are nearly bisected 

 by a bluntisb angulation, wbicb is made more marked by about 20 small, oblique, longi- 

 tudinally elongated knobs, of wbicb scarcely a trace appears below or above tbe keel ; 

 tbey become fewer up tbe spire and die out on tbe last wborl ; tbere are very many, rougb, 

 very unequal, curved lines of growtb. Tbe wbole surface is covered by coarse, unequal, 

 and very irregular tbreads, varying in tbeir direction, and interrupted by tbe longitudinal 

 lines of growtb ; tbese tbreads are most equal in tbe infra-sutural tract, wbere tbe line of 

 tbe old sinus-markings lie ; below tbe keel tbey occur alternatingly as stronger and finer ; 

 on tbe base and snout tbey are coarse, but almost disappear on tbe point ; tbey and tbe 

 suture are exceptionally independent of one anotber. Colour yellowisb porcellanous 

 wbite. Spire bigb, narrow, conical, and slopingly subscalar. Apex broken. Whorls 

 probably 9-10, ratber narrow, somewbat bollowed on tbe sboulder below tbe suture; 

 below tbe keel tbeir profile-line is straight, but contracted to tbe suture below. Tbe base 

 (wbose upper limit is defined by a very slight angulation) is conical, drawn out pretty 

 much in tbe axial line into a long, narrowisb, cylindrical, strong, and slightly reverted 

 snout. Suture a rather minute, sharp, somewhat irregular line, which does not at all 

 follow the spiral markings, but crosses these up and down in an unusually irregular 

 manner ; it is well defined by tbe concave hollow formed by the contraction of the whorls 

 above and below it. Mouth club-shaped, being somewhat angularly ovate above (with a 

 sharpish point at the top and an angulation at the keel), and prolonged below into the 

 somewhat oblique open canal, which is kept open by the oblique cutting away of tbe 

 pillar. Outer lip sharp, but strong ; it leaves the body at an acute angle and retreats 

 towards the right to form tbe sinus, which is open and near but not immediately at the 

 body : from the sinus the lip-edge advances with a strong forward convexity to tbe poiut 

 of the canal ; laterally it is also rather convex, but is contracted into the snout, along tbe 

 edge of which it is pretty straight with a somewhat oblique direction towards the left, and 

 here it is patulous. Inner lip porcellanous, smooth, narrow, cut off, and slightly twisted 

 in front, and running out at the point to a sharp edge along the canal, the point of which 

 is then rounded and patulous. H. 1*5 in. B. 0'5. Penultimate whorl, height '23. Mouth, 

 total length 07, breadth 0'23. 



In this species the generic sinus lies high and is open, which reduces to rather small dimensions 

 the little testaceous shelf which forms its upper edge and separates it from the hody-whorl ; but the 



