446 MACTRID^E. 



lini that at Spezzia it is sought for as an article of food 

 and sold with other shell-fish. According to Clark this 

 kind is called a " mud-hen " by the fishermen at Ex- 

 mouth. They burrow in stiff clay, six inches or more, 

 each individual making and occupying its own hole, and 

 forming together a honeycombing commonwealth. The 

 breadth of the shell being two inches, the length of the 

 siphons must be at least twice as great, in order to keep 

 the hole clear and have access to the water. Bouchard- 

 Chantereaux has remarked that S.piperata also requires 

 or prefers to breathe pure air ; for during the recess of 

 the tide the orifice of the lower tube is considerably di- 

 lated, and when it is placed in a vessel of water, this tube 

 is gradually stretched out so as to reach the surface, and 

 remains for some hours in that position. Pholas has the 

 same habit. The earliest account we have of the animal 

 of the present species is that by Reaumur, published in 

 the 'Memoires de V Academic' for 1710; and it has 

 lately been described by Bouchard- Chantereaux, Quoy, 

 Philippi, Deshayes, Forbes and Hanley, and Clark. I 

 have had the benefit of collating these descriptions with 

 my own notes made in 1836. Its anatomy has been 

 elaborated by Deshayes, and illustrated by twenty-two 

 finely-coloured plates, in one of the Appendices to the 

 ' Exploration scientifique d'Algerie/ The remarkable 

 structure of the hinge, typical of this genus, did not 

 escape the observant eye of Lister. The young of S. pi- 

 perata has probably been mistaken for S. tennis ; but it 

 is much flatter and broader, and wants laminar teeth. 

 Some distorted specimens, which I found in peat, are 

 contracted, and consequently more convex than usual. 



It is " La Calcinelle " of Adanson, Trigonella plana 

 of Da Costa, Venus borealis of Pennant (but not of Linne), 

 Mya hispanica of Chemnitz, Mactra Listeri and Mya 



