2 



mark. I hare also obtained it attached to the beard of the 



greater Pinna, from the depth of above 40 fathoms ; but 



I have not obtained the animal. 

 D, DENTALIS. Turt. Lin. D. Striatum. Mont. Test. Brit. 



vol. 2, p. 495. Striated Tooth Shell. Rare, found by, 



Montagu at Falmouth; and by myself attached to the 



Byssus of a Pinna. 

 D. GADUS. Mont. Test. Brit., vol. 2, p. 496, pi. 14, fig. 7. 



Montagu says it occurs at a distance from land, attached 

 to the sounding lead of ships in the Channel. On this 

 account I have ventured to class it with Cornish Shells. 



It has been supposed that the habit of this genus is to 

 remain fixed in the sand or ooze, and there to protrude their 

 organs for the purpose of laying hold on whatever food may 

 chance to come near ; retreating into the shell on the 

 approach of danger, after the manner of the Terebellae and 

 Serpulae. But the observations of Mr. Lansdowne Guilding 

 on a species which he examined in the West Indie?, tend 

 to overturn this opinion, and to displace the animal from its 

 situation in the present classification. Placed in a vessel of 

 water, observes this Gentleman, it drew itself along on its 

 side; but this may have been owing to the shallow layer of 

 sand in which it endeavoured to bury itself in the soup plate 

 which contained it, where it might not have been able to 

 assume its proper attitude. The creature moves tolerably 

 quick, by sudden interrupted steps. When disturbed it 

 retreats quickly into its shell, which has no operculum* as 

 the Serpulidae. After a time the cloak is protruded, the 

 tentacula set in motion, and the vermiform active foot par- 

 tially thrust out to explore its path. When it wishes to 

 proceed apace, the foot with its petal-shaped alae closed 

 round the stem, is protruded to its full length ; the ala3 are 

 then suddenly expanded, and the base of the foot being 

 forcibly contracted, the shell is brought forward, while those 

 expansions laid open in the sand, prevent the apex of the 

 foot from losing its advanced position. Of the place of the 

 Dentalium in the natural system, continues Mr. Guilding, 

 I will not venture to speak at this moment, though perhaps 

 we shall not do wrong, in the present state of our knowledgo 

 of the Mollusca, in placing it near the great family, or I 

 should rather say, great tribe of Linnean Patellae. In its 

 anal opening it resembles the genus Fissurella, while the 

 apicial figure represents the posterior marginal rima of 

 Emarginula. Trans. Lin. Soc. vol. 17, p. 31. 



AMPHITRITEA. 



The tube membranous or horny, more or less studded with 

 sand or fragments of Shells. 



