33G THE YOYAGE OF H.M.S. CHALLENGER 



ribs, and these continue to the point of the snout. Spirals — there is a blunt angulation 

 about the middle of the whorls ; and here the longitudinal ribs take their rise. The whole 

 surface of the shell is covered with rounded threads and furrows : on the shoulder of the 

 whorls these are rather obsolete ; on the angle among the tubercles they are strong, but 

 rather crowded ; but from this downwards they are very distinct and regular, with a few 

 finer ones interspersed, becoming a little crowded on the snout, and then sparse and 

 stronger at the extreme point. Colour alabaster-white, almost translucent from the thin- 

 ness of the shell. Spire conical, with profile-lines a little interrupted by the contraction 

 of the sutures. Apex slightly eroded, but evidently small and rounded ; the embryonic 

 whorls seem to be about two. Whorls 8 in all, of rapid increase, but that rather in 

 breadth than height ; the last is extremely large and tumid ; they have a long and gently 

 sloping shoulder above, and are cylindrical below the blunt angulation which bisects 

 them ; the last contracts slowly from the angle, and is tumidly convex on the base, the 

 curve of which sweeps on, on the right side, uninterruptedly to the point, while on the 

 left side it passes by a rather deep concave curve into the lop-sided, triangular-shaped, 

 small-pointed snout, which, however, projects very much in the line of the axis. Suture 

 strong, a little channelled from the overlap of the calcareous surface of the inferior whorl, 

 well defined from the angulation made by the meeting of the whorls. Mouth large, long, 

 angularly pear-shaped, and oblique to the axis. Outer lip very thin ; it is a high arched 

 curve, straight and steep on the shoulder, and regular from the angulation downwards : 

 the edge retreats on leaving the body, and forms a wide, deep, elliptically rounded 

 sinus occupying the whole shoulder, having above it a short triangular shelf, and 

 below, the high elbow formed here by the prominent sweep of the lip-curve, which does 

 not retreat till near the end of the snout. Inner lip is shallowly excavated in the sub- 

 stance of the shell, which rises beyond it with a slight edge ; it is broad, and winds round 

 the pillar ; the line of it is slightly convex on the body and concave at the junction with 

 the pillar, which is short and conical, obliquely cut off to a point, with a long, fine, 

 rounded, and slightly twisted edge. H. 0'95 in. B. 0'57. Penultimate whorl, height 

 0-15. Mouth, height 0'62, breadth 0'35. 



This is a very peculiar and beautiful species. The animal is so much unlike other Pleurotomas 

 as to make the classification of the species very doubtful 



66. Pleurotoma (Pleurotomella) pruina, Watson (PL XXIV. fig. 4). 



Pleurotoma (Thesbia) pruina, Watson, Prelim. Keport, pt. 9, Journ. Linn. Soc. Lond., vol. xv. 



p. 453. 



Station 78. July 10, 1873. Lat. 37° 26' N., long. 25° 13' W. San Miguel, Azores. 

 1000 fathoms. Volcanic mud. 



