MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 415 



is very much weaker ; but there is a great deal of affinity in the 

 general features of the shell. 



19. PLEUROTOMA (DrILLIa) BRACHYTONA, n. sp. (fipaxpTOVOS, 

 short.) 



St. 191. September 23, 1874. Lat. 5° 41' S., long. 134° 4' E. 

 Off Am Island, W. of Papua. 800 fms. Mud. Bottom tem- 

 perature 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, which are slightly 

 stronger than the rest, 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 angu- 

 lation 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. 

 Whorls 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 con- 

 vexly 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 



32* 



