HELICID^E. Ill 



I. Body elongate, attached to the whole length of 

 the foot ; mantle shield-like, with a small internal 

 or sub-internal shell. 



A. Mantle simply shield-shaped^ entirely enclosing 

 the internal shell. (Limacina.) 



7.1. LIMAX Fer. (Slug.) 



Body elongate, lanceolate, granular, keeled behind; 

 mantle shield-like, ovate, concentrically lined; 

 shell sub-quadrate, flat, nail-like. 



These animals have very much the external ap- 

 pearance of Arion, but they are destitute of the gland 

 on the end of the tail ; their mantle is marked with 

 circular striae instead of being granulated, and they 

 have a different nervous system ; for, according to Mr. 

 Nunneley, the infra-oesophageal ganglion is like that of 

 Arion, but the underside, instead "of having one 

 transverse fissure, has two ; so that it presents, on each 

 side of the medial line, three gangliform eminences 

 instead of two only." 



They have generally been united with the Arions ; 

 but it has lately been discovered that there are ani- 

 mals with well-developed shells that agree with the 

 Arions in character, as the Helices do with the Slugs ; 

 and it has therefore been thought better to separate 

 them by the above character into two groups, rather 

 than follow Lamarck in dividing these animals into 

 group?, by the gradually and greatly varying form of 

 the body. 



The shells are covered with a distinct periostraca. 

 It has generally been believed that shells which 

 are covered with a reflexed portion or imbedded in 



