10 CATALOGUE OF THE MOLLUSCA 



but our object at present is only to point out the most charac- 

 teristic forms. The absence of a few species of more extensive 

 range may be accounted for by the exposed character of the 

 coast. 



Our Catalogue contains altogether 394 species, divided as fol- 

 lows : — 



Cephalopoda, 6 



Gasteropoda — 



Nudibranchiata, 44 



Pellibranchiata, 1 



Inferobranchiata, 1 



Tectibranchiata, 13 



Pulmonata, 80 



Pectinibranchiata, 92 



Scutibranchiata, 3 



Cyclobranchiata, 12 



Cirrhobranchiata, 3 



249 



Conchifera — 



Palliobranchiata, 1 



Lamellibranchiata, 108 



109 



Tunicata, 30 



394 



It may be useful to give an idea of the distribution of these 

 into different zones of depth, which we shall now endeavour to 

 do by enumerating the most characteristic species in each zone. 

 We have adopted the divisions of Professor E. Forbes, contract- 

 ing a little their limits, the better to adapt them to the condi- 

 tions observable on our coast. They are as follows : — 



1. Littoral Zone. — Between high water-mark and the low 



water of ordinary tides. 



2. Laminarian Zone. — Between low water and 12 fathoms. 



3. Coralline Zone. — From 12 to 30 fathoms. 



4. Region of Deep Water. — 30 fathoms and upwards. 



