VI.] 



INTRODUCTION. 



CXI 



and formation of their dwellings, as egg-shells, or lime, 

 are to laying-hens. The shells of our common garden- 

 snail (H. aspersa) in Guernsey are remarkably thin, owing 

 to the deficiency of calcareous material ; and specimens 

 of H. pomatia, from granite formations in alpine districts, 

 are far inferior in weight to those from our chalk downs, 

 although they do not differ in size. 



Channel Isles. Some conchologists entertain a doubt 

 whether the Mollusca of Guernsey and the other Chan- 

 nel Isles ought to be included in the British fauna, 

 because of their greater proximity to the French than to 

 the English coast. The Sarnie fauna and flora (although 

 undoubtedly peculiar) have, however, been hitherto con- 

 sidered by our best naturalists as belonging to Great 

 Britain ; and our Continental neighbours have never 

 claimed them as their own, although they have appro- 

 priated Corsica, or " annexed" it to France, in a Natural- 

 history point of view. Some of the Mollusca, taken in 

 that part of the English Channel which is adjacent to 

 Guernsey, are peculiarly Southern forms and have not 

 occurred in any other part of our seas. Nearly all of 

 them are very conspicuous and handsome. They are 

 Cardium papillosum, Argiope decollata, Haliotis tuber- 

 culata, Murex corallinus, Triton cutaceus, and T. nodi- 

 ferus. Of these six species only three (viz. Haliotis tuber- 

 culata, Triton cutaceus, and T. nodiferus) are noticed by 

 either De Gerville, or Collard des Cherres, as having been 

 found on the opposite coast of Brittany ; and Bouchard- 

 Chantereaux has not included any of them in his list of 

 marine shells found on the coast of Normandy. Dr. 

 Bowerbank has identified some of the sponges from 

 Sark as northern species. In respect of geographical 

 position, some of the Channel Isles are not so very much 

 nearer France than England. Guernsey is distant about 



