PURPURIPERA. MOLLUSCA. 299 



Shell thick but light, of a livid or bluish-white color ; exclud- 

 ing the wing, it is spindle-shaped, composed of eight or nine 

 moderately convex whorls, with numerous smooth, rounded, cres- 

 cent-shaped folds, which scarcely reach the well-marked sutures ; 

 on the largest whorl there are about twenty-five folds, and on the 

 last but one they become closer and fainter, till they finally dis- 

 appear on the back ; two or three whorls at the pointed apex are 

 also destitute of folds ; beautiful revolving lines, of uniform size 

 and distance, also ornament the shell ; aperture crescent-shaped, 

 independent of the wing ; this arises a little above the suture of 

 the preceding whorl, and passes off from the spire at an angle of 

 about one hundred and twenty degrees, to a distance equal to the 

 breadth of the lower whorl ; after forming somewhat of a spur at 

 the posterior and outer angle, it advances, smooth and very thick, 

 at nearly a right angle, in a straight line nearly an inch, then, form- 

 ing an obtuse angle, passes obliquely forward to the pointed termi- 

 nation of the columella, forming with it a short, shallow, and ob- 

 lique canal ; pillar lip smooth and rounded, convex above, and 

 concave below ; throat livid ; a thick, dusky epidermis. Length 

 2J inches, breadth 1^ inch, divergence 40. 



Tips of this shell, some of them, however, wanting nothing but 

 the expansion of the lip, are all that have yet been found in our 

 Bay, and along the coast of Maine. Complete shells are found 

 in fishes taken at the Newfoundland Banks. 



It is a very extraordinary shell, resembling, in its expansion without 

 digitations, the fossil species macroptera, of which the genus HIPPO- 

 CRE'NE has been formed. The animal is not known, but from the alli- 

 ance of the shell to the Aporrhais pes-pelecani it probably belongs to the 

 same genus. As this cannot now be settled, it is better to leave it still 

 in the genus ROSTELLA'RIA, from which the pes-pelecani has been sep- 

 arated, on account of a difference in the animal. 



The lip is very remarkable, and very much resembles the lip of 

 Strombus tricornis. 



FAMILY PURPURIFERA, LAM. 



Shell with a short, ascending canal, or an oblique notch, or semi-canal, 

 directed upwards. 



