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



it is a little contracted and drawn out, and is produced into a small and rather lop-sided 

 snout. Suture minute, but impressed and further defined by the marginal thread. 

 Mouth small, narrow, pear-shaped, triangular above, and produced below into the relatively 

 broad, open, and deep canal. Outer lip flat at the shoulder, feebly angulated at the keel, 

 scarcely convex below ; the edge, which is quite independent of the ribs, is very convexly 

 prominent below, with a high and advancing shoulder, above which lies the deep, open- 

 mouthed, rounded sinus. Inner lip is exceedingly narrow ; it is thinly cut into the 

 substance of the shell, and very early runs out on the slightly oblique, narrow, twisted 

 edge of the pillar, which is straight, narrow, and very slightly angulated at its junction 

 with the body. H. 0'25 in. B. 0-09. Penultimate whorl, height 0-044. Mouth, height 

 0*13, breadth 0*04. 



Probably none of the specimens obtained of this species are quite full-grown. I have put this, 

 and the two following species, under Mangelia, not because they at all agree in sculpture with that 

 group, for they do not, but because the apex agrees better with the apex of Mangelia than it does 

 with that known to me in any other of these very perplexing and badly defined groups. I do not 

 believe that these and many other species can remain where I have put them, but as the entire 

 family is in process of disintegration they may fare with the rest. 



76. Pleurotoma {Mangelia) incincta, Watson (PI. XXIV. fig. 7). 



Pleurotoma (Mangelia) incincta, Watson, Prelim. Report, pt. 9, Journ. Linn. Soc. Lond., vol. xv. 



p. 438. 



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

 Azores. 1000 fathoms. Volcanic mud. 



Shell. — High and narrow, with rounded lines, biconical, thin, white, glossy, feebly 

 ribbed, faintly spiralled, and slightly keeled, having a high, stout, conical spire ending in 

 a blunt point, with a small long body-whorl, produced base and snout. Sculpture : Lon- 

 gitudinals — there are on each whorl about 22 slight and unequal threads serving as ribs ; 

 they are cusped at the top of the whorls, and oblique below ; on the last whorl they are 

 sinuous, but very obsolete : the ordinary lines of growth are excessively faint, except in 

 the sinus-area, where they are sharp though minute. Spirals — the suture is marginated 

 below with a very small, prominent gemmed thread ; below the plain suture-area is a slight 

 keel, beset by small tubercles where it crosses the riblets. On the body flat threads are 

 just perceptible, which increase in distinctness on the point of the base; on the snout 

 these become more raised, and are parted by intervals of two or three times their width. 

 Colour porcellanous white. Spire broadish, conical. Apex consists of 4 globose, conical, 

 yellowish embryonic whorls, whose point of union with the regular whorls is slightly 

 obscure ; the last is rather closely curvedly ribbed longitudinally, while the earlier ones 

 are polished and smooth ; the extreme tip is small. Whorls 8 in all, rather broad, with 



