79 



nomena, which are remarkable for being concentrate 1 in great num- 

 bers within the narrow limits of Jamaica, instead of being spread 

 over a continent or a zone. 



Naturalists are well aware of the perplexities, which arise from 

 facts, such as we have now alluded to, in attempting to ascertain the 

 limits of species. The question — what is a species — is easily an- 

 swered in theory. But in many classes of the animal kingdom, this 

 question is extremely perplexing in practice. It is only the laws of 

 nature which are simple ; the resultant effects present a tangled mass 

 of phenomena, which only Infinite Intelligence can fully compre- 

 hend. Many of the descriptive generalizations of organic nature, 

 like that of linear gradation, which have so much of beautiful sim- 

 plicity, have already passed away, because they originated in tlie hu- 

 man mind, and formed no part of the Divine plan. Others, like 

 those of the unity of place and parentage in the origin of species, are 

 fast disappearing. Perhaps the theory of distinct limits of species 

 may fail in some of the lower classes of animals 



We shall now be understood, when we describe the three following 

 types in the group of Helices above mentioned, without attempting to 

 decide whether the degree of difference should elevate them to spe- 

 cific rank, or reduce them to varieties of Helix sinuata. Unable 

 now to ascertain, with absolute certainty, which form was the type of 

 the original description by Miiller, we have assumed it to be that 

 which is most generally distributed through the island. 



Helix in valid a. Shell veiy convex above, somewhat flattened 

 below, with a very slight sharp carina on the periphery : dark red- 

 dish or blackish brown, paler at the apex (and after exposure, as 

 usual in the group), with a white lip, and a white line along the pe- 

 riphery : surface finely granulated, except on the upper whorls of the 

 spire and around the umbilical region : spire much elevated : whorls 

 five, moderately convex, with a lightly impressed suture : aperture 

 like that of 11. sinuata, but rather smaller, with the lip and teeth 

 less robust, the right pair of teeth a little more connected at base, 

 and their exterior indentations shorter : umbilicus wanting. This 

 shell is much smaller than the common type of H. sinuata. 



Greatest breadth .78 inch ; least breadth .GGinch; height .46 inch. 



Helix propenuda. Shell like H. sinuata, but the color is very 

 pale, almost white except on the upper whorls : the aperture more 

 contracted ; the exterior furrows are very short, and the right pair of 

 teeth a little joined at base : the epidermis consists of small distant 



