404 MURICID^. 



The varieties of this species have received especial 

 attention from Professor King, Mr. Albany Hancock, Mr. 

 Howse, and other naturaUsts, to whose papers we must 

 refer for details of greater length than can be included 

 in our space. Within the littoral zone, usually at its 

 lowest verge, and mostly on the northern coasts, extend- 

 ing its range sometimes into the laminarian zone, is the 

 smallest form, that to which the term littorale has been 

 applied. It lives equally on mud, sand, and rock, and 

 we have met with it abundantly on all these grounds in 

 the Frith of Forth. It is a ventricose dwarf shell, with 

 a short spire, sometimes strong, sometimes thin, undulated, 

 or without undulations ; in the former case usually living 

 on rocks or hard shores, and then its surface is without 

 an epidermis ; iu the latter, living on sand or mud, and 

 having an epidermis, which is frequently highly pilose. 

 In deeper water, ranging from the middle of the lami- 

 narian zone to as deep as thirty or more fathoms, where 

 the ground is hard or roughish we find a very strong, 

 often ponderous shell, with prominent and often angulated 

 undulations, and the surface unprotected by an epidermis. 

 This is the variety crassum of King, who mentions 

 his observation of its passage into his variety magnum. 

 The spire is moderately produced, the spiral sulcations 

 strongly marked, and the colour of its aperture usually white. 

 The variety into which it passes has the epidermis more 

 or less developed and often quite glabrous, the substance 

 not so thick, and the undulations not so strongly marked, 

 diminishing in intensity, indeed, until at length, usually 

 in comparatively thick shells, they disappear entirely on 

 the body-whorl, when we have the striatum of Pennant, 

 a form which is common, and grows to a large size on 

 the scallop banks off the north of the Isle of Man. This 



