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cess and (Icficioney in describing new species. We hope eventually 

 to describe all the kindred facts, which we have observed, since the' 

 have important relations to the general questions of the limits, origin, 

 and permanency of species. Similar observations by Mr. Chitty 

 coincide with my own, and are more numerous than my opportunities 

 have permitted me to make. 



Almost every one of the numerous districts in Jamaica, which are 

 favorable for the terrestrial Mollusca, has one or more peculiar mod- 

 ifications of the type of that group of Helices, which is represented 

 by Helix sinuata. In some instances, these subordinate local types 

 are accompanied by a type which has a more general distribution. 

 In other cases a local type exists alone. 



Some of these local types are so ?pj(/e/y distinguished from the gen- 

 eral type, that no one hesitates to regard them as good species. Such 

 are H. anomala, H. strangulata, and H. tridentina. Less different 

 from the typical species are II. Schroeteri, H. Bronnii, H. valida, and 

 H. picturata. Other local types present an inferior quantity, but an 

 almost equal constancy, of difference from the typical species. In 

 the latter case, he who is not acquainted with their distribution and 

 has not the means of observing their constancy, may be confident that 

 such forms are mere varieties. On the other hand, an observer, 

 whose attention should be wholly occupied with these phenomena, 

 would be likely to make almost as many species as there are local- 

 ities. 



In some instances the peculiarities of a local type, which differs 

 but slightly from the typical species, are quite constant at the given 

 place, but vary geographically, that is are gradually lost in the more 

 and more distant individuals. I am not aware that these examples 

 are numerous. 



Not only does the amount of difference between the local types 

 vary from that of well marked species to that of scarcely distinguish- 

 able varieties, but the individuals of a given locality, while preserving 

 the peculiarities of the type, sometimes differ from each other in 

 characters which appear to be as important, except in the want of 

 constancy, as those which distinguish the local group. 



Similar to the above is the case of the Naiadai of the United 

 States, and to a greater or less extent of many tribes of Mollusca in 

 in other widely extended regions. These remarks might be extend- 

 ed to many classes in other divisions of the animal kingdom ; but our 

 object, at present, is merely to notice an example of a class of phe- 



