BUCCINOID^E ; FUSUS ; STROMBUS ; PLEUROTOMA. 385 



that of the Murex and its allies, which are distinguished by the 

 great length of the siphon, as well as (in many instances) by 

 the remarkable prolongation of the shelly canal in which it is 

 protected along a part of its course. This is nowhere more 

 remarkable than in the Murex itself (Fig. 559). Frequently, 

 however, the shelly canal is not itself prolonged ; as is the case 

 in the Pteroceras (Fig. 560). To this group belong a consi- 

 derable number of large shells. The Fusus much resembles the 

 Murex ; but has none of those ridges or 

 varices, which mark, in the latter, the 

 lines of successive addition to the shell. 

 In like manner, the Strombus is allied to 

 the Pteroceras ; being distinguished, like 

 it, by a great extension of the lip, when 

 adult age is reached ; but this lip is desti- 

 tute of the long finger-like processes, which 

 are so remarkable in that shell. The 

 accompanying figure of the Pleurotoma, 

 another genus belonging to the same group, 

 is here introduced for the purpose of 

 explaining the names which are given by 

 Conch ologists to different parts of a shell, 

 and which are made use of in the scien- 

 tific description of it. At a is seen the 

 canal for the passage of the siphon ; b, 

 a hollow, here nearly closed up, termed 

 the umbilicus; c, the internal edge or 

 left lip, which is partly formed by the 

 columella ; d, the external or right lip, 

 the edge of which is free ; e } the notch 

 or slit, which is peculiar to this genus ; /, 

 the sinus ; g, part of the last turn of the 

 spire, which is called the venter or belly ; 

 h, h, the turns or whorls of the spire ; i, the sutures, or lines of 

 union between these. 



FIG. 582. PLEUROTOMA 

 BABYLONICA. 



