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214 Mr. Gray's Conchological Observatiotis. 



^ 7. On the Epiphragma. 



The Epiphragmais a membraneous or chalky substance secreted 

 by the animal, and closing the aperture of the shell in winter, and 

 in very dry weather during the summer. It is peculiar to the land 

 shells, or Pulmoniferous Mollusca, A^'ith retractile tentacula and 

 pedicled eyes. As soon as the animal becomes sensible of the 

 approach of either cold or drought, but more especially of the for- 

 mer, he retreats within his shell and secretes a quantity of mucus- 

 like substance, which gradually becomes harder and covers the 

 outer extremity of the retracted body. It has generally a small 

 triangular mark over the aperture near the hole in the edge of the 

 mantle, which conducts the air into the respiratory cavity. Some- 

 times, as in the Helix Pomatia, candidissima, See. the whole of the 

 Epiphragma becomes shelly; in this case the animal forms a second 

 membraneous covering, more internally, at some little distance 

 from that first formed, and exactly similar to the external cover- 

 ing of the other species. On the approach of warm and damp 

 weather the animal secretes a small quantity of mucus, which 

 loosens the adhesion which had taken place between the Epi- 

 phragma and the sides of the aperture, and the former is thrown 

 oflf by the pressure of the animals foot. When another is required, 

 the whole process is commenced anew. 



Various names have at different times been given to this part. 

 The ancient authors called it ni^a, KaXf/x^a, and 'Ew/xaXu/*fta. 

 Thus Dioscorides called the Helix naticoides, which is remark- 

 able on account of its large convex lid, nufMna ; and Gesner, 

 for a similar reason, gave the name Pomatia to the shell which 

 we now call Helix Pomatia, which has been whimsically trans- 

 lated into Jpple or Orchard Snail. Lister, with his character- 

 istic accuracy, designated it as Operculum saliva covfectum, and 

 Muller distinguishes it from the true opercula by the name of 

 Operculum hybernum. Draparnaud, according to the French 

 custom, has given it the new but very expressive name of Epi- 

 phragma ; and Montague the inaccurate one of Hybernaculum. 

 I was inclined to adopt the former of the above names, but Dr. 

 Goodall informs me that it was used also for the true operculum. 



