MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 519 



close-set, slightly oblique grooves, which look as if they were 

 turned in a lathe. Further down the shell they become shal- 

 lower, and cease at last rather abruptly. The flat bands of the 

 ■ shell-surface which part them are of variable width, and increase 

 with the growth of the shell from about O'Oll to twice that 

 amount. The front part of the shell is closely, minutely, ob- 

 liquely striated in the line of growth, with here and there a very 

 faint depression, just suggestive of the grooves above. There 

 is besides these a faint transverse flocculence in the substance 

 of the shell. Mouth-edge thin, not contracted, very slightly 

 oblique. The apex is abruptly broken across, and there the edge 

 of the shell is thick, and from the opening there projects a 

 minute round pipe about O'OOS broad, and 0-012 long, slightly 

 striated obliquely, abruptly broken off at the end. In most 

 of the specimens only the mere stump of this delicate tube 

 remains. L. 0-55. B. 0-038, apex O'OIS. 

 This species seems to vary a little in breadth. 



SlPHODENTALIUM. 



1. S. platmnodes, "W. 5. S. diclielum, "W. 



2. S. tyttJium, W. 6. S. prionotum,'^ . 



3. 8. pusillum, W. 7. S. ehoracense, W. 



4. S. tetraschisfiim, W. 



1. SiPHODENTALIUM PLATAMODES, W. (TrXarafxwSrjs, as flat on 



the sides.) 

 St. 24. St. Thomas, ]S'. of Culebra Island, Danish "West Indies. 



390 fms. Mud. 4 specimens. 



Shell. — Small, solid, finely tapered, curved, especially toward the 

 apex, five-sided, with four sharp corners, which are nearly right 

 angles, and one very obtuse angle along the concave curve ; 

 these all tend to disappear toward the apes, the young shell 

 being rounded. Sculpture. The angles of the shell project more 

 or less in a sharp rounded rib, which is sometimes double ; there 

 are a few longitudinal striae, regular, 0*01 in. apart, strongest 

 near the angles, more or less obsolete as they recede from these. 

 Neither end is fresh enough for description. L. 0'47. B. 

 0049. 

 I have hesitated a good deal in separating this from S. tetrago- 



num, ^roc., = quinquangulare, E, For., with which it agrees more 



