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Cji. XL. 



MIGRATION OF TESTACEA. 





all tlie eig'lit regions^ namely^ Area lactea and Ceritliium 



lima. 



^ 



^ ^ 



i 



Great range of some provinces and species. — In Europe con- 

 cliologists distinguish between the arctic fauna, the southern 

 boundary of which corresponds with the isothermal line of 

 82° F., and the Celtic^ which, commencing with that limit as 

 its northern frontier, extends southwards to the mouth of the 

 English Channel and Cape Einisterre, in France. Erom that 

 point begins the Lusitanian fauna, w^hich, according to the 

 observations of Mr. M*^ Andrew in 1852, rai ^ 

 Islands. The Mediterranean province is distinct from all 

 those above enumerated, although it has some species in 

 common with each. 



The Indo-Paciiic region is by far the most extensive of all 

 It reaches from the Red Sea and the eastern coast of Africa, 

 to the Indian archipelago and adjoining parts of the Pacific 

 Ocean. To the geologist it furnishes a fact of no small 

 interest, by teaching us that one group of living species of 

 moUusca may prevail throughout an area exceeding in mag- 

 nitude the utmost limits we can as yet assign to any assem- 



Mr. 



umm 



4- 



blage of contemporaneous fossil species. 

 tained more than 100 species of shells from the eastern coas 

 of Africa identical with those collected by himself at the 

 Philippines and in the eastern coral islands of the Pacific 



mi 



from pole to pole. 



Certain species of the genus lantliina have a very wide 



common 



They are all provided with a beautifully contrived floaty which 

 rp.nders them buoyant, facilitating their dispersion, and 

 enabling them to become active agents in disseminating other 

 species. Captain King took a specimen of lanthina fragilis 

 alive, a little north of the equator, so loaded with barnacles 

 (Pentelasmis) and their ova that the upper part of its shell was 

 invisible. 



Helix pidris {Succinea piitris^ Lam.) has a wide range in 

 Europe, occurs also in Siberia, and is said to inhabit :New- 



* Eeport to the Erit. Assoc. 1843, p. 130. 



t Quart. Joiirn, Geol. Soc, 1846, vol. ii. p. 268. 



