52 ESSAY ON CLASSIFICATION. 



Gopher (Testudo Polyphemus, Auct.) of our Southern 

 States; and among Fishes, by the Blind Fish (Amblyopsis 

 spelceus) of the Mammoth Cave. Examples of closely 

 limited Articulata may not be so striking; yet the Blind 

 Crawfish of the Mammoth Cave, and the many parasites 

 found only upon or within certain species of animals, are 

 very remarkable in this respect. Among Mollusks I would 

 remark the many species of land shells, ascertained by 

 Professor Adams to occur only in Jamaica, 1 among the 

 West India Islands; and the species discovered by the 

 United States Exploring Expedition upon isolated islands 

 of the Pacific, and described by Dr. Gould. 2 Even among 

 Radiata many species might be quoted, among Echino- 

 derms as well as among Medusae and Polypi, which are 

 only known from a few localities; but, so long as these 

 animals are not collected with the special view of ascer- 

 taining their geographical range, the indications of travel- 

 lers must be received with great caution, and any gene- 

 ralization respecting the extent of their natural areas would 

 be premature, as long as the countries they inhabit have 

 not been more extensively explored. 3 It is nevertheless 

 true, as established by ample evidence, that, within defi- 

 nite limits, all the animals occurring in different natural 

 zoological provinces are specifically distinct. What remains 

 to be ascertained more minutely is the precise range of 

 each species, as well as the most natural limits of the dif- 

 ferent faunae. 



1 ADAMS (C. B.), Contributions to 3 With reference to the Echino- 

 Conchology; New York, 1849-50, 8vo. derms and Acalephs, I am able to 

 A series of pamphlets, full of original state, that the species of the Atlantic 

 information. shores of North America, found along 



2 GOULD (A. A.), Mollusks, United the northern states, differ entirely 

 States Exploring Expedition, under from those of the southern states, and 

 the command of Cu. WiLKES,U.S.N.; these differ again from those of the 

 1 vol. 4to., Philadelphia, 1854. Gulf of Mexico. 



