INTRODUCTION. XIX 



thought fit to create three more, for the reception of certain 

 species which had points in their anatomy differentiating them 

 from the species with which they had been placed. 



In that very specialized division of the animal kingdom, the 

 Land-Mollusca, and particularly in the family Zonitidae, great 

 uniformity of the general main structure obtains with at the same 

 time very remarkable variation of the several parts, particularly 

 those of mastication and generation; it maybe safely said that 

 in some genera a greater amount of variation is met with in the 

 internal organs than is to be found in the form of the shell. 

 When we come to compare molluscous animals from far distant 

 parts of the world, either proceeding from east to west, or from the 

 Northern to the Southern Hemisphere, we find each land-area has its 

 own distinctive set of genera. Fossil evidence again shows some 

 have had in the past a much more extended range, and it becomes 

 evident they have gone through a remote, extremely slow, and 

 separate evolution. This is, after all, not so remarkable when the 

 great antiquity of the Pulmonate Mollusca is considered : land- 

 shells extremely like those of the present day go back to the 

 Palaeozoic period, being first known from the Devonian, and to- 

 gether with other life on the earth demand many subsequent eras 

 for their specialization. 



While the Vertebrates have been classified scientifically by 

 their internal anatomy, Invertebrates such as the Mollusca 

 have received comparatively desultory notice. For this reason 

 Dr. Blanford in arranging for the publication of a volume on the 

 Land-Mollusca decided to incorporate all that was known of the 

 animal. 



Many years must elapse before the necessary material can be 

 got together to elucidate and advance the knowledge of the 

 generic relationship of these Indian land-shells. In the case of 

 the ZonitidsB, it happens a large number of very fragile shells are 

 found differing very slightly from each other in shell-character, 

 yet on examination of the animal such marked differences are 

 presented that they have to be placed in separate genera ; in 

 fact satisfactory determination is quite uncertain without a 

 knowledge of the animal. 



Space will not admit of dealing with the anatomy in any great 

 detail ; I have therefore only attempted so much as seems desirable 

 to give the collector some idea of the position and function of the 

 different parts, from which he will more readily understand that 

 the shell alone is of very uncertain value in all questions relating 

 to phylogeny or relationship, evolution, and range in connection 

 with problems relating to the former distribution of land and sea. 



BODY AND FOOT. 



Animal soft and flexible, covered with an epidermis which in 

 the land forms secretes much mucus from an elaborate system of 

 not only mucous, but sensory and pigmentary glands, rendering 



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