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



Sliell. — Small, depressedly conical, sharply carinate, and spirally lirate, umbilicate, 

 smooth. Sculpture : There is a sharp carina at the periphery ; above this is a spiral 

 liration formed by a sharp angulation, which on the upper whorls lies near the suture, 

 but on the later whorls lies nearer the carina. The carina is margined below by a broad, 

 shallow, round furrow, which is defined on its inner side by a sharp spiral thread. The 

 umbilicus is defined by a sharp thread, outside of which is a shallow furrow and two or 

 three more spiral threads ; the centre of the base is nearly smooth, but has also some 

 feeble spirals, which increase in strength toward the outside and toward the centre. 

 Besides these, the whole surface is covered with sharp, not approximate, microscopic 

 spirals. Longitudinals — there are numerous distinct lines of growth, which on the 

 second whorl are like minute radiating spokes, and in the superior sinus {i.e., between 

 the suture and the first spiral) are sharp and distinct, and more remote than elsewhere 

 on the surface, except on the base round the umbilicus, where, though less sharp, they are 

 even more distinct. Colour a dead chalky white, with an exquisite pearly nacre below 

 the outside layer and within the shell. Spire low and scalar. Avex flattened, the 

 embryonic lj whorl, though a little tumid and large for the genus, being somewhat 

 immersed. Whorls 7, of regular and slow increase until the last, which increases rather 

 more rapidly ; angulated above, tumid on the base, where (unlike Seguenzia carinata, 

 Jeffr.) the edge of the umbilicus is the most projecting part. Suture linear, very 

 minute, but defined by a very slight shelf, which projects horizontally just below it. 

 Mouth perpendicular, squarish, but too much broken for description. Outer lip, the lines 

 of growth show it to have the same three sinuses as those described in Seguenzia mono- 

 cingidata, Seg. Pillar-lip patulous, a little reverted, scarcely twisted, with a broad deep 

 sinus above, a strong, but not sharp, twisted tooth projecting at about three-fourths of its 

 length, below which is a smaller sinus running out into a point at the extreme end of the 

 pillar. Umbilicus large, funnel-shaped, deep, sharply defined by the edge of the base, the 

 spiral of which runs out to the point of the pillar-lip. Within the umbilicus is a strongish 

 undefined spiral furrow answering to the pillar-tooth, and the lines of growth are strongly 

 defined. H. 0-18 in. B. 0-24; least breadth 0-21. Penultimate whorl 0-04. 



This species differs from Seguenzia carinata, Jeffr., in being more depressed and broader, much 

 more angulated and more lirate above, more tumid and lirate below ; the carina is less flanged, and 

 the most prominent part of the base is the edge of the umbilicus, not the centre of the whorl ; here, 

 too, the last whorl and the mouth are larger. The young of this species look disproportionately small 

 and high. 



3. Seguenzia carinata, Jeffreys (PL VII. fig. 2). 



Seguenzia carinata, J. Gwyn Jeffreys, Biol. "Valorous" Cruise, Proc. Roy. Soc, No. 173, 187G, p. 201. 

 „ „ "Watson, Prelim. Report, pt. 3, Journ. Linn. Soc. Lond., vol. xiv. p. 590, sp. 3. 



Station 73. June 30, 1873. Lat. 38° 30' N., long. 31° 14' W. W. of Azores. 1000 

 fathoms. Pteropod ooze. 



