476 THE OCEAN WOKLD. 



of Mexico ; -a total -of fifteen hundred species is enumerated by Pro- 

 fessor Adams as belonging to the province. 



The Transatlantic province, or that on the coast of the United 

 States, does not afford a large number of species, only two hundred 

 and thirty being known ; of these, only fifteen are found in Europe. 



The study of the terrestrial and fresh- water mollusca affords even 

 better grounds for their division into provinces; but we shall not 

 enter into it here, as it belongs to the Land World. 



We shall now say a few words on the depth of the sea, or ocean, in 

 which Mollusca are found. 



The observations of Milne Edwards, Audonin, and Professor Edward 

 Forbes, have led to the division of the sea into four zones. 



The deep sea Coral zone, from fifty to one hundred fathoms ; the 

 Coralline zone from fifteen to fifty fathoms ; the Laminarian zone, 

 which stretches from fifteen fathoms to low water ; and the Littoral 

 zone, between high and low water marks. The great stronghold of 

 Crania, Thetis, Neaera, Yoldia, Dentalium, and Scissurella, is in the 

 deep sea Coral zone; while Buccinum, Fusus, Pleurotoma, Natica, 

 Aporrhais, Philine, and Velutina, which are among the most ravenous 

 and predatory of molluscs, are found in the Coralline zone. They 

 attack the bivalves, whose shells among the relics of former seas, as in 

 those of the present, show evidence of an assault and a murder. 



The principal genera of the Laminarian zone are the Nudibranchiata, 

 Aplysia, Trochus, Nacella, Kissoa, and Lacuna, which feed so much on 

 the seaweed of this region. 



The Littoral zone, which being accessible as the tide recedes, is 

 best known, affords Cardium, Mytilus, Tellina, Solen, Trochus, Patella, 

 Littorina, and Purpura ; or in plain English, cockles, mussels, razor- 

 fish, limpets, periwinkles and tingles ; species which are the first to 

 attract our attention, and which are so much used for food. 



