114 MANUAL OF NATURAL HISTORY. 



Like other animals, the Mollusca obey certain 

 laws, and offer peculiarities in their geographical 

 distribution. Thus, as we approach the equator 

 from the poles, we find their size, beauty, and va- 

 riety, gradually increase ; the species are also more 

 numerous near the shores, but perceptibly diminish 

 as the water deepens ; and, in like manner, the 

 land shells are large and abundant in the valleys, 

 and become smaller and less in number as we 

 ascend the mountains. Rivers, lakes, ponds, and 

 springs are peopled by numerous tribes, as the Am- 

 pullarice of South America ; the Melanice of the 

 East Indies; and iheLimncei of Europe. The pela- 

 gian forms are found in all oceans, as the lanthina, 

 the Carinaria, and the Argonaut. 



In the Northern Seas the shells are of a dingy 

 hue, and often covered with an epidermis, while in 

 the tropics they often vie in splendour with the 

 fishes, and are sometimes highly polished. The 

 Mediterranean and the surrounding regions are very 

 rich in Mollusca, the number of species of Glausilia 

 being especially great ; the deserts of Africa give 

 sustenance to few species, but what are known are 

 of a peculiar character ; while the rivers also yield 

 singular types, such as JEtheria and Galathea ; in 

 South Africa we observe the great Achatince, and 

 the sinistral Lanistes ; while the Cape of Good 

 Hope is famous for its species of Patella. The 

 shells of the Canary Islands and of the Madeiras, 

 are nearly all of a peculiar stamp ; and the West 

 Indies harbour an abundance of forms, each island 



