PULM0N1FERA. 5 



The Pulmoniferous Inoperculated Cephals are distributed into 

 three Families : — 



1. Limacinea. Respiratory and visceral organs incorporated with 



the main contractile mass of the body. Eyes at the extremity 

 of the tentacles. Shell wanting, or rudimentary. 



2. Colimacea. Respiratory and visceral organs distinct from the 



main contractile mass of the body, coiled within a spiral 

 shell. Eyes at the extremity of the tentacles. 



3. Auriculacea. Respiratory and visceral organs distinct from 



the main contractile mass of the body, coiled within a spiral 

 shell. Eyes at the base of the tentacles. 



Family I. LIMACINEA. 



Respiratory and visceral organs incorporated toith the main contractile 

 mass of the body. Eyes at the extremity of the tentacles. Shell wanting, 

 or rudimentary. 



The typical character of the Family of Limacinea is expressed by 

 the respiratory and visceral organs being incorporated with the 

 main contractile body of the animal, as distinguished from that of 

 the Colimacea and Auriculacea, in which they are coiled within a 

 whorled shell. In the simplest terrestrial form of mollusk, Avion, 

 Geomalax and Limax, the pulmonary sac is situated near the head, 

 with slight variations in the position of the respiratory orifice. In 

 Testacella it is situated at the tail end of the animal. There is an in- 

 termediate form of slug, Parmacella, in which the pulmonary sac is 

 situated about the middle of the body ; but this is a stranger to our 

 islands, not having reached nearer to us than the south of France, 

 at Axles in the department of the Mouths of the Rhone. 



In these three genera of Limacinea there is no visible shell, but 

 the calcifying function commences to be developed in the shield 

 covering the pulmonary sac, with the secretion of a few calcareous 

 grains. In Avion they are at first isolated, then agglomerated in a 

 rude mis-shapen manner. In Limax an embryo umbonal nucleus is 

 formed ; and the shell, in a further stage of development, increases 

 in symmetrical order by regular concentric layers of growth, covered 

 by a membranous epidermis. In the fourth genus, Testacella, the 

 shell is secreted externally, and the umbonal nucleus commences to 



