MOLLUSCA OF THE ' CHALLENGER' EXPEDITION. 591 



opaque white, but even then showing barely the faintest 

 trace of pearly nacre. Spire conical, rather depressed, and 

 with a slight convexity of its contour-lines. Apex very small 

 and sharp, flattened on the one side, and with the minute em- 

 bryonic IJ whorl projecting roundly on the other. Whorls 

 7. of gradual increase, slightly convex above, flatter below, 

 and a very little constricted above the sutural flange, whoso 

 edge is sharp below and rounded above. The base projects 

 rather sharply from the inner side of the carinal flange, and 

 then passes rather flatly across to the edge of the umbilicus, into 

 which it slopes steeply. Suture linear and a very little impressed. 

 Mouth perpendicular, almost square, but a little rounded both 

 on the sides and at the angles. Outer lip sharp and thin, not 

 patulous, not descending ; the curves of its edge are similar to 

 those described in S. formosa, there being three sinuses, one 

 near the suture, a second at the carina, and a third toward the 

 exterior of the base. Pillar-lip is patulous and a little reverted, 

 scarcely twisted, with a broad deep sinus above, a strong twisted 

 projecting tooth 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. JJmhilicus large, funnel-shaped, deep, defined by 

 a fine spiral thread, which runs out to the point of the pillar-lip ; 

 within the umbilicus is a shallow furrow answering to the 

 pillar-tooth, and above is another spiral thread, stronger, but 

 less sharp than that on the edge ; the curved lines of growth are 

 strongly defined in the umbilicus. H. 0'15. B. 0*17, least 

 015. Last whorl 0-037. Mouth, height 0*049, breadth 0*5. 

 This species is so thin and transparent that scarcely any trace 

 of nacre can be recognized ; but by carefully occluding the light 

 on the outside, and thus having* all the light reflected from the 

 inside of the mouth, the pearly lustre is distinctly visible, especi- 

 ally at the outer upper corner. 



4. Seguenzia trispinosa, 



St. 120. Pernambuco. September 9, 1873. Lat. 8"^ 37' S., long. 



34°28'W. 675 fms. Mud. 12 specimens, old and young. 



Shell. — Small, high, conical, scalar, with three rows of tubercled 

 lirations, umbilicate, thin, smooth. Sculpture. There is a 

 sharp circumbasal carina, above this is a broad shallow fur- 

 row ; about one third up the whorl is a narrow and blunt 

 liration ; a little more remote is a third, separated by a 

 * From the three rows of spinous lirations. 



