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



58. Pleurotoma (Perrona) marmarina, 1 "Watson (PL XXIV. fig. 8). 



Pleurotoma (Perrona) marmarina, Watson, Prelim. Report, pt. 9, Journ. Linn. Soe. Lond., vol. xv. 



p. 429. 



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

 350 fathoms. Eed mud. 



Shell. — Biconical, ribbed, barely tubercled, spirally furrowed, and compressedly banded 

 below the scarcely impressed suture, with a high pointed spire, a short lop-sided base, 

 and a very short snout. Sculpture: Longitudinals — there are on the last whorl 15 

 rather narrow, spread-out, rounded, scarcely oblique direct ribs, which begin at the upper 

 suture and extend to the base, but not to the snout ; near the top they are cut by a spiral 

 furrow, so that the upper part of them forms a series of small rounded tubercles just below 

 the suture ; below the spiral furrow the ribs are slightly swollen into knots ; the ribs are 

 parted by wider shallow furrows : these ribs and furrows run pretty regularly down the 

 spire ; but there are fewer of them on the earlier whorls. The whole surface is further 

 scored by almost microscopic regular hair-like lines of growth, which are specially sharp 

 in the sinus-area. Spirals — there is a furrow near the top of the whorls, which constricts 

 both the ribs and the interstices. On the last whorl there are 18 or 20 shallow and 

 narrow furrows parted by flat interstices of about three times their width ; these do not 

 extend to the sinus-area, and only very doubtfully to the snout, where there are rather a 

 few irregular and scarcely raised rounded threads : these furrows are not recognisable on 

 the earlier whorls. The whole surface is very delicately fretted with almost microscopic, 

 crisp spiral striae, whose course is not quite regular, and which are crimped or disturbed 

 by the lines of growth ; this sculpture is particularly sharp and distinct in the sinus- 

 area. Colour pure marble-white. Spire very regularly conical. Apex : there are about 

 two embryonic whorls, which are small, nearly cylindrical, with scarcely appreciable 

 suture, and end in a blunt, round, laterally flattened-down tip. Whorls 10 in all, rather 

 short and broad, scarcely at all convex ; the last is large, being broad and tumid, but not 

 long, with a tumidly conical lop-sided base, ending in a short, broad, flat snout which is 

 abruptly and cut off straight. Suture linear, but well defined by the swelling of the 

 infrasutural row of tubercles. Mouth oval, with an acute angle above, an obtuse angle at 

 the side where the body and pillar join, and a truncation at the point. Outer lip thin, a 

 little patulous, with an equable convex curve throughout : the sinus is very shallow and 

 round, with no shelf above it ; and below it is a very high but little prominent shoulder 

 made by the very slightly advancing lip-edge. Inner lip very narrow, shallowly hollowed 

 into the substance of the shell ; the pillar is straight, conical, and is obliquely cut off in 

 front with a blunt, rounded, scarcely twisted edge. H. 0"66 in. B. 0'29. Penultimate 

 whorl, height 0*12. Mouth, height 0'3, breadth 0'14. 



1 paonaym, gleaming like rnarble. 



