466 PELOEID^E. 



by placing the strong corneous operculum well within the 

 margin; it has nothing of the rapid retraction of the foot, 

 as in Rissoa. 



These animals abound of large size in the Warren Sands, 

 opposite Exmouth. When just taken, in vigour, and im- 

 mersed in sea- water, it is scarcely possible to contemplate a 

 more beautiful and interesting object, with its shell rising as 

 a globular pyramid from an immense circular disk, elegantly 

 marked with fine dark lines on a clear drab ground. I re- 

 commend this species for examination ; its large size affords a 

 good view of the external organs, and the anatomy is compa- 

 ratively facile. 



N. NITIDA, Donovan. 



N. nitida, Brit. Moll. iii. p. 330, pi. 100. f. 2,3,4-, (animal) pi. P.P. 



f. 5 (as Alderi). 

 N. Alderi, nonnull. 



This species, as regards the external organs, is so similar to 

 the N. monilifera, that a notice of the variations will suffice. 

 It has, like its congener, two branchial plumes, and the 

 mucous fillets are nearly as evident as in the Muricida. In 

 the male, the organ of reproduction is in every respect more 

 developed. The eyes are distinctly visible, immersed in the 

 centre of the anterior bases of the tentacula. The colour of 

 the upper front surface of the foot and tentacula is a deepish 

 dull red-brown, which is deposited on the first-named organ 

 in close, irregular, longitudinal streaks, but on the posterior 

 portion they are more distant and paler coloured, and still 

 more so laterally ; the sole is a uniform pale yellow. These 

 animals vary much in the general colour, but whatever the 

 ground colour may be, it is modified on the particular parts 

 as above stated. 



The animal is active and not uncommon in the coralline 

 zone at Exmouth, where, though very rarely, the pure snow- 

 white variety occurs, as well as the plain chestnut- coloured 

 N. sordida. 



