standing water, and where no rivers flow, or where the rivers without 

 obstruction and with no material change of course run through the 

 base of lofty mountains. In the dense and varied tropical vegetation 

 above, and in the innumerable places of retreat beneath the surface, 

 we find the paradise of snails. They, with a variety of articulated 

 animals, form a guanoid soil, which renders the almost naked rocks 

 the most fertile spots and sustains a thorny and impenetrable vege- 

 tation. 



The difference in the extent of the marine and of the terrestrial 

 species is remarkable. A few of the marine species of Jamaica 

 occur also in the New England States ; and many are found in the 

 Southern States. Several occur in West Africa, and in the Med- 

 iterranean, and a large majority are already known to occur through 

 the other islands. Perhaps we may safely conjecture that not more 

 than ten or fifteen per cent, of the marine species are peculiar to 

 the island. The same law governs those genera of Colimacea which 

 are maritime in their habits, viz. Truncatella, Pedipcs, and Me- 

 lampus. 



With the species of Mollusca, which are strictly terrestrial, the 

 law of distribution is reversed. Probably not more than six to nine 

 per cent, of the species are common to any other islands. In the 

 Thesaurus Conchyliorum of G. B. Sowerby, Jr., Cydostoma artic- 

 ulatum is said to have come from Demerara and the Antilles; and 

 the habitat of HcUcina picta Fer. is said to be Martinique and 

 Jamaica. The habitat of H. hajmastoma Moric. and of C. Adamsi 

 Pfr. (C. crenulatum Gray) is 'the Antilles,' and yet more generally, 

 C. fascia Gray and H. neritella Lam. are said to come from the 

 West Indies.* Thus of the 97 operculated species, two only (with 

 a third which we have not enumerated as a Jamaica shell) are af- 

 firmed to occur in other islands. 



Of the HELiciD.Et of Jamaica, the genus Geomclania has been 

 found only in Jamaica. Of Cylindrclla, C. brevis is said, by Dr. L. 

 Pfeiffer on the authority of Petit, to occur in Martinique, and Cuba 

 is doubtfully mentioned as its habitat. Variety C' of C. Humboldti- 

 ana, and variety y of C. variegata, both Cuban species, are said by 

 Dr. Pfeiffer to occur also in Jamaica. C. Maugeri, a Jamaica species, 

 is said by Dr. P. on the authority of Dr. Hornbeck, to occur also in 

 St. Thomas. The remaining thirty species are peculiar to Jamaica, 



* Cyclostoma Sauliac was introduced erroneously into the Catalogue on 

 page 16, No. I. 

 t See catalogue of species, page ?0. 



