53 



of the land shells which inhabit Jamaica are of less size than either 

 of these ; viz. Helix apex (No. 41,) Pupa Jamaicensis (No. 44,) 

 and Achatina iota (No. 38.) The latter is probably the least of all 

 the known species of terrestrial molluscs. Two others (Nos. 19 and 

 40) are of the same size as Pupa milium. 



It follows that the least of all known terrestrial shells exist in 

 tropical regions. A subsequent investigation of the size of the ma- 

 rine species, which we have collected in Jamaica, will also show a 

 large number of extremely minute shells. From the well known 

 fact that the larger species occur only in tropical regions, it has by 

 many been too hastily inferred that only temperate regions contain a 

 large proportion of very small species. The difference of zones is 

 not that one extreme of size is found in the tropics and the other in 

 temperate climates, but that, while both appear in tropical countries, 

 one extreme is deficient in temperate regions. 



Within the tropics, however, there appears to be a great difference in 

 the average size of the land shells of different regions. In the West 

 Indies and in the Polynesian Islands, there is a great proportion of 

 small species. But in Brazil and in the Philippine Islands, there 

 are very few small land shells. It is remarkable that this purely 

 geographical difference greatly exceeds the average difference in the 

 species of different zones. The cause of this prominent fact in the 

 plan of creation it may not be easy to discover. 



Description of a supposed new species of Columbella. By C. B. 

 Adams, Jan. 1850. 



Columbella ovdloides. Shell long obovate : yellowish brown, 

 rarely blackish brown, irregularly mottled with large angular spots of 

 white, often with a band of white around the middle of the last whorl, 

 with the apex white : with numerous fine spiral striae, of which those 

 that are on the upper part of the whorls and at the anterior extremity 

 of the shell are coarser ; with excessively minute unequal stria; of 

 growth : apex acute : spire with very concave outlines : whorls nine, 

 the penult whorl only being very convex, with a well impressed su- 

 ture, which near the end is rapidly curved upwards towards the apex : 

 aperture very long and linear : labrum much produced in a broad 



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