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



edge, which is sharp throughout, retreats at once, forming a very narrow and short ledge 

 between the body-whorl and the sinus, which is rounded and open, and whose depth is 

 due entirely to the great forward sweep of the lip below, where it projects like the pinion 

 of a wing and is slightly patulous ; it curves in laterally to the origin of the canal, and 

 then advances very straight and scarcely patulous to the rounded point of the shell. Inner 

 lip is slightly cut out of the substance of the shell, is very narrow and very straight, the 

 cutting away of the point of the pillar being very gradual and very slightly oblique. H. 

 1*13 in. B. 0-33. Penultimate whorl, height - l 2. Mouth, total height CK58, breadth 0*16. 



The tubercled angulation of this species recalls faintly a similar feature in Pleurotoma nivalis, 

 Lov., Norway and Britain, and Pleurotoma plebcia, "Wats. It is slightly like Pleurotoma uni/asciata , 

 Sow., from West Columbia, but is much longer in the canal. It is very near to Pleurotoma dimidiata, 

 Broc. (a sub-Apennine Miocene species), of which there are specimens (perhaps the Pleurotoma 

 powerii, Calcara, which Labassi holds to be a variety of Pleurotoma dimidiata) as slim as the 

 Challenger species ; but in Brocchi's species the keel is sharper and persists to the mouth-edge ; on 

 the same length of shell it has two whorls less ; from the suture, which is not in the least impressed, 

 the whorl, before expanding to the carina, descends in a cylindrical or even slightly contracting 

 form ; the surface is a little roughened with slightly raised threads ; the lines of growth run from 

 the suture forward at first toward the left, not, as in the Challenger species, at once to the right into 

 the sinus ; and the embryonic whorls are more rounded, with a deeper suture and half a whorl 

 fewer. It extremely resembles Pleurotoma undata, Lam., an Eocene fossil from Grignon ; but has 

 the spire more attenuated, the suture rather deeper, while the tubercles on the keel do not, as there, 

 become longitudinal ribs, and the snout is much longer. It is this last feature distinctively which 

 excludes the species from the Typhlomangclia group. 



22. Pleurotoma (Surcida) hemimeres, 1 Watson (PI. XXV. fig. 10). 



Pleurotoma (Surcida) hemimeres, Watson, Prelim. Report, pi 8, Journ. Linn. Soc. Lond., vol. xv. 



p. 398. 



Station 120. September 9, 1873. Lat. 8° 37' S., long. 34° 28' W. Off Pernambuco. 

 675 fathoms. Eed mud. 



Shell — High, conical, with a small, round-tipped conical apex ; ribless, but with a 

 keel beset with longish narrow tubercles. Sculpture: Longitudinals — there are only fine 

 hair-like lines of growth. Spirals — about f down each whorl is a very sharp and promi- 

 nent angulation, and the keel thus formed is beset by numerous small, sharpish, narrow 

 and elongated tubercles, which fail to become ribs; of these tubercles there are about 12 

 on the earlier whorls, and they become more numerous on the succeeding whorls. Below 

 this keel there is a straight-lined contraction ; above it there is a long, slightly concave 

 shoulder, with a delicate row of small tubercles at the top close to the suture. Both rows 



1 q/ii/tfipis, halved. 



