MOLLUSCA or THE ' CHALLENGER ' EXPEDITION. 697 



■weaker is close up to the suture ; the second is a little lower thaa 

 tlie middJe, and its tubercles are strong. Of these there are ou 

 each row twenty to twenty-five ; they are scarcely connected by 

 a spiral thread. The periphery is sharply angulated and defined 

 by an expressed and tubercled carina, the tubercles of which are 

 hardly so strong as those of the second row above, which from 

 its larger points projects quite as much as the carina. On the 

 base there is an infracarinal furrow and three or four sharpish, 

 equally parted, faintly tubei-cled, spiral threads, the inmost of 

 which is most distinctly tubercled, and defines the umbilical de- 

 pression. Longitudinals — the apical whorls, except the embry- 

 onic one, are crossed by high, sharp, slightly oblique ribs ; but 

 these on the later whorls break up into tubercles, between which 

 on the different rows there is a slight irregi;lar connexion by flat- 

 tened ridges, which are oblique, interrupted, and on the base 

 sinuous. Besides these the surface is roughened by minute 

 wavy irregular lines of growth. Colour white, with a translucent 

 layer of porcellanous glaze over brilliant pearly nacre. Sjpire 

 high. Apeco small, flattened, with the minute inflated 1\ embry- 

 onic whorl rising a little exserted on one side. Whorls 7, pro- 

 jecting out squarely below the suture, flattened in the middle, 

 protuberant at the second row of tubercles, and slightly con- 

 tracted above the carina ; at the carina sharply angulated. 

 The base, which is flatly rounded, has a narrow flattish margin, 

 and in the middle a slight umbilical depression, in the centre of 

 which is a minute umbilical hole almost covered by the pillar-lip. 

 Suture linear. Mouth scarcely oblique, and very slightly inclined 

 out from the axial line, squarish, but rounded on the base and at 

 the angles, a little broader than high, nacreous within. Outer 

 lip not thin, with a slight callus just within it ; it is slightly 

 sinuated on the base at the outer corner. Pillar-lip, on leaving 

 the body, bends over very flatly so as to cover the umbilicus, after 

 which it curves round to the left ; it has a very blunt tubercle 

 in the middle, is a little reverted, and has a very slight furrow 

 behind it. Umbilicus a small open depression leading into a minute 

 central pore. The slopes of the depression are obliquely scored by 

 the tubercles of the central basal thread. H. 0'22. B. 0'16, least 

 0-15. Penultimate whorl 005. Mouth, height 0-06, breadth 0-07. 

 This beautiful little shell offfers some rather perplexing features ; 

 for the curves of growth on the base indicate a slight sinus to- 

 ward its outer edge, which, indeed, is shown in the actual mouth- 



