324 THE VOYAGE OF H.M.S. CHALLENGEE. 



54. Pleurotoma (Spirotropis) brachytona, 1 Watson (PL XVIII. fig. 3). 



Pleurotoma {Drillia) brachytona, Watson, Prelim. Keport, pt. 9, Journ. Linn. Soc. Lond., vol. xv. 



p. 415. 



Station 191. September 23, 1874. Lat. 5° 41' S., long. 134° 4' E. Off the Arrou 

 Islands, south-west of Papua. 800 fathoms. Green mud. Bottom temperature 39° - 5. 



Shell. — Short and broad, biconical, angulated, thin, with small oblique riblets and 

 spiral threads, and with a lop-sided, small-pointed snout. Sculpture: Longitudinals — 

 on the last whorl there are about twenty small, short, oblique riblets, which are obsolete 

 on the base ; they are parted by shallow furrows somewhat broader than they : they are 

 more numerous and sharper on the upper whorls, where they occupy the whole lower 

 third of each whorl. Immediately below the suture there is a minute collar of very small, 

 short, sharp, irregular puckers with intervals of twice their own breadth : springing from 

 these puckers and coinciding with the riblets are hair-like lines of growth, slightly stronger 

 than the other growth lines which closely cover the whole surface of the shell. Spirals 

 — there is a slight collar at the top of the whorls, which forms a very minute and irregular 

 shelf on the underside of the suture ; about two-thirds down the whorls is a blunt angula- 

 tion where the longitudinal riblets rise. Besides these, there are on the whole surface 

 flatly rounded threads which are broad, coarse, and irregular on the base, crowded and 

 narrow at the keel, broader, but faint and more regular, on the shoulder. Colour alabaster- 

 white. Spire irregularly conical. Apex eroded. Wliorls 8, making allowance for the 

 eroded apex ; they have a long, sloping, slightly concave shoulder, a blunt angulation 

 about two-thirds down, and below this are nearly cylindrical : the fifth whorl enlarges 

 somewhat disproportionately ; and the last whorl is swollen, with a sharper angulation 

 than the rest ; the base is convexly conical, and is produced into a lop-sided, centrally 

 situated, small-pointed snout. Suture small but distinct, being slightly channelled by the 

 minute horizontal shelf formed by the edge of the infrasutural collar : there is a very slight 

 contraction of the whorls into it. Mouth rather small, rhomboidally pear-shaped, being 

 pointed above, prolonged into the rather short and broad canal below, and having a blunt 

 angulation in the outer lip and at the base of the pillar. Outer lip very thin : it is 

 somewhat rectilinearly curved ; its edge, on leaving the body, retreats immediately 

 to form the shallow rounded open sinus which occupies the shoulder below the suture. 

 Below this it advances with a long oblique forward slope in the line of the riblets, and 

 then, from about the middle, retreats on a very regular curve to the point of the pillar. 

 Inner lip is a thin glaze with a defined edge ; it is very narrow on the body, but spreads 

 round the pillar; it is convex on the body, with a bluntly angular concavity at the base 

 of the pillar, which is short, small, conical, unequal-sided, obliquely cut off in front, with 



1 /3»a^urc>oj, short. 



