46 



limited, and by ascertaining a wider distribution of some which are 

 now known. The validity also of several of the species which have 

 been enumerated in the preceding catalogues is even more than 

 doubtful, as intimated in the captions of the articles. Additional 

 specimens and the suggestions of experienced zoologists will enable 

 us, we hope, at some future time to determine more satisfactorily 

 many of these difficult and doubtful cases. With some confidence, 

 however, in the general correctness of the following views, we think 

 it unnecessary any longer to withhold them. 



A fact, which affects the visiter from a northern climate with 

 astonishment, is the great profusion of the terrestrial species, and 

 their accumulation in certain districts. In the parish of Manches- 

 ter, a region four miles long and one mile wide contains one hun- 

 dred species, — as many as the whole number native in North Amer- 

 ica east of the Mississippi river. After becoming acquainted with 

 their stations and localities, a collector might easily obtain eighty 

 or ninety species in one day, for most of them are sufiiciently nu- 

 merous in individuals to render his success certain with ordinary 

 skill. Of the 265 terrestrial species which have been enumerated, 

 more than two hundred were collected by the writer in person in a 

 hasty exploration of one-tenth of the surface of Jamaica. From 

 the very limited distribution of most of these species, we may rea- 

 sonably expect that this island, 6400 square miles in extent, will 

 furnish from 350 to 400 good species. Long might a collector 

 continue his explorations, and make good his maxim — nulla dies 

 sine specie. 



It should not, however, be supposed that the species have been 

 distributed, in such profusion, over all parts of the island indiscrim- 

 inately. The trappean, syenitic, and sandstone districts are as des- 

 titute of land shells, both of species and of individuals, as the 

 barren surface of New England. In the limestone districts, but 

 few species will be found on the Newer Pleiocene (?) or rubble 

 limestone. They abound on the more perfectly consolidated lime- 

 stone of Meiocene (?) age. Here the numerous and violent dislo- 

 cations of the earth's crust by earthquakes, for a long succession of 

 ages, have broken the surface into innumerable cavities and laby- 

 rinthine passages. These have been only partially filled with soil, 

 since the mechanical decay of the well consolidated limestone is slight, 

 and no glacial agency has ever smoothed down the asperities of the 

 surface. Extensive districts occur where tropical rains leave no 



