THE SNAIL TRIBE 



33*7 



opening, and thus make it, one would suppose, a matter of some difficulty for the 

 animal to squeeze through them when emerging from its shell. Vertigo is a genus 

 similar to Pupa as regards the shell, but separable on account of the animal having 

 only one pair of tentacles, the lower pair being entirely wanting. The shells, 

 according to the species, are dextral or sinistral. Clausilia is remarkable for 

 the large number of species, the general similarity in the form of the slender 

 shell, and the peculiar process within it, which serves as a door to shut in 

 the animal when retracted. The shells are almost invariably reversed, and fur- 

 nished with two or three folds or plicae within the mouth, and other lamellae still 

 further within, which can only be detected by the transparency of the shell it- 

 self. About a thousand species have been described. They are most numerous 

 in Europe and Eastern Asia, only a very few species being known from South 

 America. Achatina is one of those genera the scope of which has been greatly 



-VAX 



AGATE SNAII, (Achatina fulica). 



altered since it was first founded by Lamarck. In those days any land shell with 

 a notch or truncation in the pillar lip of the aperture was considered an Achatina. 

 It is, however, now reserved for a group of large snails which are only met with 

 in Africa, Madagascar, and a few other adjacent islands. They have fine hand- 

 some shells, vividly painted with more or less wavy stripes, and covered with 

 a thin periostracum. A. variegata, in the tropical forests of West Africa, is 

 sometimes seven and a half inches in length, and the largest of all the living land 

 shells. 



The members of the extensive family Achatinellida are inhabitants of the 

 Sandwich islands, and occur in no other part of the globe; the species being all 

 small, and many of them both dextral and sinistral. Some are found on trees 

 and shrubs, while others are always met with on the ground. Mr. Barnacle has 

 given an interesting account of the production of musical sounds by these little 



