480 MUEICID^E. 



which the eyes are placed externally ; from thence the tenta- 

 cula taper conically to their extremities. The mouth is a 

 vertical fissure beneath the tentacular veil, and emits the 

 characteristic proboscis. The foot when quiescent is nearly 

 oval, but on the march is truncate in front, throwing off on 

 the right and left small auricular points; it is gently con- 

 stricted medially, and has a blunt rounded termination, 

 carrying on the posterior upper surface an elongated, red- 

 brown, corneous, unguiculated operculum. 



Lamarck's commentators say, that between the genera 

 Murex and Purpura there are sufficient marks of distinction, 

 and, in support of this opinion, they adduce the truncation of 

 the tentacula at their offsets in Purpura, which they state is 

 more apparent than in Murex. We dissent from these views, 

 and think the distinction is purely ideal at least it is so in 

 the species of each genus we have examined : the fact is, that 

 when the tentacula are collapsed, the basal two-thirds appear 

 very tumid and broad at the termini of the offsets, but in fully 

 extended action the truncation nearly or altogether vanishes, 

 and no peculiarity is apparent at these points. 



It will be observed below, that the external organs of 

 Murex lapillus, the Purpura of authors, are nearly identical 

 with those of M . erinaceus, and the internal organs of the 

 two are so similar, that it would be a repetition to describe 

 them. The corneous opercula scarcely show distinction ; that 

 of this species may be generally of a deeper red, and somewhat 

 rounder, though the arches of the striae are not less elliptical. 

 The gland producing the purple dye is as conspicuous as in 

 M. lapillus ; indeed this gland may be traced in all the 

 Canalifera, though its secretion varies in colour ; there may 

 also be a slight difference in the lingual riband, which is here 

 rather longer and more coiled than in its congener, and the 

 cerebral ganglia are smaller : but these variations are of little 

 value. The different hues of brown in Murex erinaceus form 

 the ground colour, but are invariably mixed with white or 

 flaky-yellow markings on the upper part of the foot and on the 

 tumid portion of the tentacula, the conically-pointed upper 

 parts being of a uniform colour ; the under part of the foot is 



