196 AMERICAN JOURNAL 



Professor described, of the Jamaica fauna, besides a large num- 

 ber of marine species, upwards of two hundred and fifty spe- 

 cies of land and twenty of fresh- water shells, very few of 

 which proved to have been previously known. 



The descriptions are framed with the greatest care, the pecu- 

 liarities of the species nicely distinguished, and their affinities 

 discussed. As a remarkable example of critical investigation, 

 we would refer to the Professor's "Analysis of the Group of 

 Species of Cychstoma, which is represented by C. Jamaicense^ 

 Chem." ("Contributions," pp. 140—148.) 



In "Remarks on the Distribution of the Terrestrial and 

 Fresh-water Mollusca which Inhabit Jamaica," ("Contribu- 

 tions," pp. 45 — 50, 1849,) the Professor comments on the great 

 profusion of the terrestrial species, and their accumulation in 

 certain districts. He says, that, of the 265 species enumerated 

 iu his Catalogue, more than 200 were collected by himself in 

 a hasty exploration of one-tenth of the surface of the island, 

 and that a collector, after becoming acquainted with their sta- 

 tions and localities, might easily obtain eighty or ninety spe- 

 cies in one day. 



The study of the Jamaica shells directed, at an early period, 

 the attention of Professor Adams to the general questions of 

 the limits, origin and distribution of species. He refers to the 

 perplexities which arise in attempting to ascertain the limits 

 of species from such facts as he observed in the group of 

 Selices represented by Helix sinuata, several of which facts 

 he thus specifies: — 



"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 grad- 

 ually lost in the more and more distant individuals. I am not 

 aware that these examples are numerous. 



"Not only does the amount of difterence between the local 

 types vary from that of well marked species to that of scarcely 

 distinguishable varieties, but the individuals of a given lo- 

 cality, while preserving the peculiarities of the type, some- 

 times 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." ("Contributions," p. 78, Feb., 

 1850.) 



Subsequently the views of the Professor on these questions 

 became more developed, and were published especially in his 

 "Remarks on the Origin of the Terrestrial Mollusca of Ja- 

 maica," ("Contributions," pp. 85—87, March, 1850,) andin a 

 paper entitled "On the Nature and Origin of the Species of 

 the Terrestrial Mollusca in the Island of Jamaica," ("Contri- 

 butions," pp. 189—194, Nov., 1851.) 



