76 PHOLAS. 



to the surface, it opens a passage for itself by means of 

 its testaceous shield, which it moves on all sides, and 

 by which alone it mounts to the surface of the sand, &c. 



M. Giceni then describes the manner in which the 

 animal moves, by pressing the end of his shield against 

 the sand, and thus obtaining a point of support, while 

 he slowly drags the rest of the body after him. But 

 this operation is so painful, and is executed so heavily, 

 that the animal leaves a trace behind it, from the impres- 

 sion of the great valves, in the sand, which resembles in 

 miniature the track of carriage wheels ! ! The calcula- 

 tion of the time which the animal takes to move along 

 the sand, is admirable. M. Giceni reckons it at the 

 twelfth part of an inch in eight seconds ! Much more 

 of a similar detail equally absurd is entered into by the 

 Italian naturalist; but enough has been said to prove the 

 falsity of the rest. The circumstantial manner in which 

 the whole has been related, however, and the accurate 

 figures, (for they are accurate as far as relates to the 

 gizzard of the J3. lignaria,) with which the account is 

 illustrated, has misled Retzius, who, in a tract entitled 

 Nova Testaceorum Genera, published in 1788, has de- 

 scribed the trivalved gizzard, under the name of Tricla 

 Giceni ; and Bruguiere has formed a new genus of it, to 

 which he has added a long description from Giceni, 

 under the word Char, in the Eticyclopidie Methodique. 

 It is also figured as a new genus, after Pholas, in pi. 

 170. of the same work. 



The gizzard of the B. lignaria is well described and 

 figured by Mr. Humphrey, in the second volume of the 

 Linnaean Transactions, page 15. 



