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



ridge. Sculpture: Longitudinals — there are fine, sharp, pretty close- set, curved, radiating 

 riblets, which are nearly equal above and below the canal ; between these in the furrows 

 there are fine lines. Spirals — fully one-half of the last whorl is keeled by the canal-ridge, 

 which forms a crest round the top of the whorl a little within the periphery ; its outer edge 

 is slightly overhanging, its inner edge raised a very little ; the canal is narrow, and sinks 

 between these two edges : it begins in a small oval and ends in a tumid swelling, in which 

 is a small oval hole, sharp-pointed in front. This hole is not cut in the shell after that 

 has been formed, but is developed along with it, the lines of growth conforming to the 

 foramen. The hole is continued within the shell by prominent lips, and a strong little 

 furrow is carried in the substance of the shell from the hole on to the ed°e of the 

 outer lip. This furrow is marked outside by a very slight ridge, but still more by the 

 interruption of the riblets, which curve sharply back, becoming at the same time very 

 faint. The whole surface is scored and the riblets serrated by sharp, fine, remote threads, 

 between each two of which towards the mouth a weaker similar one appears. Spire quite 

 flat. Apex very small, slightly depressed. Whorls 3 to 3^, of very rapid increase ; above 

 they are barely convex, on the base they are tumid. Suture slightly impressed. Mouth 

 large, round, very oblique. Outer Up very descending, flat above, well curved and patulous 

 below : it is continued, as in Lacuna, by a sharp keel, which runs straight up into and 

 encloses the umbilicus, but does not include its outer edge. Inner lip short but strongish 

 and defined on the body ; it very patulously overhangs the umbilicus, with a broad 

 rounded furrow between its sharp umbilical edge and its inner rounded border ; the sharp 

 umbilical edge runs straight down to join the outer lip on the base, and the inner border 

 runs down within the basal lip, flattening out into a very slight callus. L. 0'055 in. B. 0083. 

 Mouth, length 0-053, breadth 0-047. 



2. Schismope lacuniformis, n. sp. (PI. VIII. fig. 8). 



Station 24. March 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. Off Culebra 

 Island,West Indies. 390 fathoms. Pteropod ooze. 



Shell. — Obliquely, flatly globose, very finely striated longitudinally and spirally, with 

 rounded whorls, a very small, slightly raised apex, barely impressed suture, very large gib- 

 bously round mouth, large lacuniform 1 umbilicus, and a mere dot of a fissure. Sculpture : 

 the whole surface is striated with very fine, slightly raised, distant, very oblique longitudinal 

 threads, and with very similar spiral threads, which are a little finer and closer, but on the 

 upper whorls relatively stronger ; these longitudinals and spirals (the latter on the top) 

 cross one another, but not at right angles, and do not form tubercles at their intersections. 

 Spire short, slightly raised. Apex very small, prominent ; the first whorl and a half seem to be 



1 Hence the name. 



