214 Mr. Gray's Conchologicnl Observations. 



§ 7. On the Epiphragma. 



The Epiphragma is 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 laad 

 shells, or Pulmoniferous Molliisca, Avith retractile tentacula and 

 pedlcled 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, &c. 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 

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

 the whole process is commenced anew. 



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

 The ancient authors called it na)/xas, K«Ay/AfA«, and 'E7r/xa^t;/A/4a. 

 Thus Dioscorides called the Helix naticoides, which is remark- 

 able on account of its large convex lid, riw/xar/a ; and Gesner, 

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

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

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

 istic accuracy, designated it as Operculum saliva confecium^ and 

 Muller distinguishes it from the true opercula by the name of 

 Operculum hijbernum. 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, 



