OPE AS. 355 



found in cultivated areas, are as local as most other laud snails. 

 Owing to the similarity of the shells, their determination is 

 difficult, and demands the greatest application. 



" Opeas stands very close to the groups Prosojieas and Curv-cUa. 

 The former diifers by merely such minor features as the rougher, 

 often minutely lameilose sculpture, the greater size and flatter 

 whorls, but these give the shell a rather different aspect. CurveUa 

 in its typical form diifers by the short and Bulimoid shape ; but 

 some of tlie species are arbitrarily referred to one or the other 

 genus. The distinction between Opeas and Gtirvella is by no 

 means convincing ; yet even small differences have significance 

 which may usefully be recognized in dealing with large groups of 

 similar species. 



" Opeas and Sahulina begin to reproduce before the shell 

 has attained its full size, usually when it is about two-thirds 

 growu. 



" In many species two forms co-exist in the same colony, 

 a more slender and a stouter ; all other features remaining the 

 same. Intermediate contoni's usually occur if a large gathering 

 is at hand. This dimorphism must be kept in mind, especially 

 when dealing \\ith small sets. 



"Excepting a few forms spread by commerce or other means, 

 the Old and New World species are distinct. Most of the 

 Eastern forms belong to typical Opeas. 



" Several species in each hemisphere have been enabled, b} 

 their hardiness and adaptability to life in cultivated areas, to 

 colonize over a large part of the tropical and subtropical zones. 

 There cannot be much doubt that the carriage of living plants 

 from place to place has been a chief factor in the dispersal of 

 Opeas .... and other snails as well. The habits of these forms 

 are such that they find practically the same environment anywhere 

 in zones of similar temperature, and their spread from new 

 centres is often very rapid. Opeas r/racile is probably the most 

 widely distributed land siuiil in the world." (Pihbr)/.) 



I have quoted at some length from the admirable account of 

 this difficult genus by Professor Pilsbry, which sets forth all the 

 known facts in an extremely lucid fashion. His observations 

 witli regard to dimorphism — to which he is, I believe, the first to 

 draw attention — are particnlarly valuable, and should be borne in 

 mind by every couchologist when about to describe supposed new- 

 species. 



317. Opeas gracile, Hutton. 



Xi). 5, BulimiisV, Hutton, .1. A. S. B. iii, 1834, p. 84; No. o, 

 Biilimn^'i (mihi) (jracilis'r, ibid., torn. cit. p. 93; Pfeiffer, Moii. 

 Ilelic. Viv. ii, 1848, p. 157 ; Reeve, Conch. Icon, v, 1849, Buli- 

 mns, pi. 69, tig. 49o; Blanford, J. A. S. B. xxxiv, 1865, p. 94 ; 

 Pfeiffer, Conch.-Cab., BuUntuK, 1853, p. 79, pi. 21, figs. 18, 19; 

 Ilanlev & Theobald, Conch. Ind. 1 870. pi, 23, fig. 4 ; Godwin- 

 Austen, J. A. S. B. xlv, 1876, p. 317. 



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