FAMILY COLIMACEA. 33 



With, reference to this species in the cocoon, Mr. Jeffreys says, 

 on the authority of some experiments made by Mr. Norman, " While 

 in the encysted state, a thin white membrane, a development of the 

 mantle, is extended from beneath the shell, and stretched over the 

 back and sides of the animal. An admirably designed protective 

 shield is thus formed, which checks evaporation from the surface of 

 the body, and enables the flow of mucus, which is so essential to the 

 life of the animal, still to course along the lateral canals, and thence 

 be distributed through the branching channels over the entire sur- 

 face of the body. When T. Mangei is removed from its cyst and 

 the body moistened with water, the extended membrane is gradually 

 contracted until it is entirely withdrawn beneath the shell." MM. 

 Gassies and Fischer do not believe, apparently, in this separate or- 

 ganization of an enveloping mantle-membrane. 



Family II. COLIMACEA. 



Respiratory and visceral organs distinct from the main contractile mass 

 of the body, coiled toithin a spiral shell. Eyes at the extremity of the 

 tentacles. 



The above definition applies to all our inoperculated air-breathing 

 mollusks, except the thirteen Limacinea just described, and the 

 four Auriculacea which follow. They are sixty in number, and 

 are the outlying members of a fauna twenty times as numerous, 

 which has its centre of creation in Southern Europe, and spreads 

 over Asia in an easterly direction to the Himalayas. Of the four 

 principal genera, Helix, Clausilia, Ptipa, Vertigo, there are certainly 

 eight hundred European to forty British species. The transition be- 

 tween the two famibes of Limacinea and Colimaeea is shown in 

 Britain by a solitary species, Vitrina pellucida, of which there are 

 only six in Europe, but upwards of seventy in the more tropical 

 parts of the eastern hemisphere. It is curiously intermediate in 

 structure between Limax and Zonites, having the fleshy shield of 

 the former along with the mantle-polished shell of the latter. With 

 Testacella, which is an abnormal form of Limacinea, the relation- 

 ship is more with a genus unknown to British soil, Daudebardia, 

 in which the respiratory orifice is situated towards the posterior 

 part of the animal, where it is covered by a horny spiral shell, not 



D 



