38 TESTACEA. 



gliding, always active when brought to the Ught. It swims supine, and 

 so it ascends as high as possible in the vessel. 



Perhaps this creature feeds on the Lobularia. Small portions of 

 mussel within reach disappeared, and some shells have been emptied of 

 their limacine tenants. 



There are some peculiarities about it which I cannot explain. I 

 thought one protruded a brownish stout proboscis. Specimens have sur- 

 vived a considerable time, several months, in my possession. — Rare. 



Plate V. 



Fig. 9. Natica Alderi. 



10. Another specimen. 



11. Shell, back. 



12. Shell, front. 



T K C H U S. 



Naturalists afHrm that it is often difficult to distinguish the subjects 

 of this genus from those of the Turbo ; but the shell is more conical and 

 elevated, and the operculum more horny. 



I shall not embarrass myself Avith very nice distinctions in these 

 miscellaneous observations. 



1. Trochus cinerarius. — Plate VIII., Figs. 1, 2. 



This is one of the more ornamental of the Scotish shells, both in 

 form and colour. It grows to about eight lines in diameter, is of a grey 

 colour, and darkly striated, so as to present the appearance of a reticu- 

 lated surfiice. 



The animal is approximated by general resemblance to the Liraax. 



Head roundish, with the mouth conspicuous below.- Two long, 

 .slender, active, variegated tentacula issue from sockets with a dilateable 

 edge, wherein they are retractile. 



