36 MOLLUSCA FROM THE CRAG. 



the common recent shell that I have no doubt of its identity. Var. a, probably B. 

 striatum, Pennant, appears to be rather of an aberrant form in this species ; the 

 outer lip is similarly sinuated, but not periodically thickened, and the consequent 

 absence of the undulatory elevations upon the body of the shell gives a great 

 apparent difference to this variety. The figures above referred to are of course the 

 extreme forms, but I think they can be fairly connected by the series I possess. 

 The proportionate dimensions of the aperture, with regard to the axis of the shell, 

 is a character by no means constant. 



Purpura,* Adanson, 1757. 



Buccinum (spec.) Linn. 



Gen. Char. Shell ovate, thick, and strong ; spire generally short, sometimes 

 elongated; external surface striated, sulcated, muricated, granulated, or tuber- 

 culated ; aperture ovate, somewhat dilated ; outer lip crenated, occasionally 

 dentated within; columella usually flattened; base subcaniculate or emarginate. 

 Operculum corneous, with a lateral nucleus. 



Shells of this genus are generally very thick and strong, and may be distin- 

 guished from Nassa or Buccinum by a peculiar flatness upon the columella, while 

 they resemble those genera in many other characters. The canal is short, straight, 

 and not reflected ; but the animal is said to present several constant characters, by 

 which it may be considered as distinct. 



It is not yet known as an Eocene fossil, though M. Deshayes speaks of it as 

 from some beds of the Oolitic period. 



1. Purpura lapillus. Linn. Tab. IV, fig. 6, a — h. 



Purpura lapillus, var. a, crispata. S. Wood. t. 4, fig. 6, a. 



- b, BREVIS 



C, ELONGATA 



d, VULGARIS 



e, ANGULATA 



/, CABIN ATA 



g, IMBRICATA 



k, INCRASSATA - 



- i, compressa, t. 19, fig. 12, a, b. 

 Buccinum lapillus. Linn. Syst. Nat. p. 1202, 1/66. 

 Tritonium lapillus. Mull. Zool. Dau. Prod. 244, 1776. 

 Purpura lapillus. Lam. An. sans Vert. torn, vi, 1815. 

 Buccinum crispatum. J. Sow. Min. Conch, t. 413, 1823. 



INCRASSATUM - - - t. 414, fig. 2. 



* Purpura, " the shell-fish from which purple is taken." The celebrated dye of the ancients is now 

 considered to have been produced from the Murex trunculus, a shell common in the Mediterranean, and 

 not from the Purpura lapillus, which is not known in that part of the world. 



f This is from the cabinet of Mr. Lyell. 



fig- 



6, 



b. 



fig. 



6, 



c. 



fig- 



6, 



d. 



fig- 



6, 



e.f 



fig- 



6, 



/ 



fig- 



6, 



9- 



fig- 



G, 



h. 



