MOLLUSCA OF THE ' CHALLENGEB ' EXPEDITION. 



589 



have put a query; tor ibougli 1 cannot separate them, still the 

 longitudinal sculpture is stronger, and there is an umbilicus. 



2. Seguenzia ionica, W.^ 



St. 24. Culebra Island. St. Thomas, Danish W. Indies. 

 390 fms. Mud. 7 young specimens. 



St. 73. W. of Azores. June 30, 1873. Lat. 38° 30' N., long. 

 31° 14' W. 1000 fms. Glohigerina-ooze. 2 specimens and frag- 

 ment. 



Shell. — Small, depressedly conical, sharply carinate, and spirally 

 Urate, mnbilicate, smooth. Sculpture. There is a sharp carina at 

 the periphery ; above this is a spiral liration formed by a sharp an- 

 gulation, 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 shaljow 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 di- 

 stinct 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. Apex flattened, the embryonic 1| whorl, though 

 somewhat tumid and large for the genus, being somewhat im- 

 mersed. Whorls 7, of regular and slow increase until the 

 last, which increases somewhat more rapidly ; angulated above, 

 tumid on the base, where (unlike S. carinata) the edge of the 

 umbilicus is the most projecting part. Suture linear, very 

 minute, but defined by a very slight shelf, which projects hori- 

 zontally 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 

 S. formosa. Pillar-lip patulous, a little reverted, scarcely 

 twisted, with a broad deep sinus above, a strong, but not sharp, 

 * So called from its resemblance to the volute of the Ionic capital. 



