so7ne of the Land Shells of Cuba. 497 



latter difficulty is, the species are so variable, that their limits 

 are almost conjectural. We have had examples of this, 

 among the few shells here noticed, in the large species of 

 Helicina and Pupa, and in Helix gilvus, Cubensis and penicil- 

 lata. Nothing but careful and extensive observation of the 

 shells with the animals and their distribution, in their actual 

 habitat, by competent naturalists, can remove this difficulty. 



Were it now a suitable opportunity, some of the animals of 

 the marine species might also be here given. 1 cannot for- 

 bear, however to allude to one instance of confusion among 

 authors. 



Deshayes remarks, in his edition of Lamarck, (vol. ix. p. 

 206) that he has completed the synonymy of Liitorina nodu- 

 losa, by uniting with it the Litt. tuberculata of Menke and 

 the Turbo trochiformis of Dillwyn ; and says that these three 

 names have been imposed upon the same species. But the 

 truth is, two shells, generically different, have been con- 

 founded by all authors which I have consulted, the one a 

 Trochus, and the other a Littorina, They live in company, 

 and their external appearance is so nearly alike, that they 

 would not be distinguished by a slight examination, though 

 the distinctive marks are unequivocal when once observed. 

 The one has a slightly developed columella, a thin lip, and a 

 multispiral operculum ; the other has a broad, somewhat ex- 

 cavated columella, and a subspiral operculum. The former is 

 figured by Wood as Turbo tuberculatus, and is evidently the 

 shell had in view by Deshayes, and is a Trochus. The latter 

 is a Littorina. D'Orbigny, in Sagra's Cuba, has figured both, 

 with the opercula even, under the genus Littorina, with dif- 

 ferent specific names, and has added still further to the con- 

 fusion by making a third species, Lit. dilatata, of superannuated 

 specimens of the Littorina with a remarkably flattened and 

 broad columella. 



The Littorina is a more solid shell, lighter colored, and its 

 tubercles are whitish ; the aperture is somewhat produced into 

 a channel. The foot of the animal is oval, while that of the 



56 



