CHAPTER LXIV: THE LAND SNAILS. HELICES 



Family HELiciOy^ 



Shell a well developed spiral; lip smooth, or drawn in by a 

 row of teeth: animal withdraws wholly into shell; jaw strong, 

 usually orange-coloured, coarsely or finely ridged; central tooth 

 of radula tricuspid; laterals, tricuspid or bicuspid; marginals 

 usually wider than high, short, with two or three small cusps. 

 Sexes united, but cross-fertilisation is necessary. A family of 

 few genera and a multitude of species, all air breathers, and ter- 

 restrial, distributed all over the world. 



The study given by conchologists to this great group of shells 

 during the past few decades well illustrates the passing of the 

 conchologist from the cabinet to the laboratory. I would better 

 say back and forth between them. At first the shell alone was 

 the basis of classification. But here is a variable family. Shells 

 of the same species show very different coloration and markings. 

 The study of the jaw became the basis for a new system of classi- 

 fication. But the jaw was found to be an unstable character. 

 Shell and jaw alone lead to an artificial system of classification, 

 and do not help to solve the problems of origin and relationship 

 of species. Studies of the anatomy of the soft parts have thrown 

 much light upon the subject. 



The assembling of the species of Helices filled eight volumes 

 of the "Manual of Conchology." in Volume IX. Pilsbry dis- 

 cards the older classification and declares for a new, natural 

 system based upon the development of the shells and of several 

 unrelated sets of internal organs. The genitalia and dentition 

 are emphasised. 



Under the new classification the Helices are reduced to about 

 fifty genera. Of these the largest and most beautiful are tropical. 

 The United States has representatives of several genera — our 

 tommon land snails, dull in colour and of small size. The Philip- 

 pines, Mauritius and the East and West Indian Islands have the 

 showiest forms, the handsomest of which live in trees. Ground 



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