GENERAL NOTES. / 



and Bivalves coexisted with those ancient Tetrabranchiates ; but 

 these types abounded more in the later geological epochs, many 

 Tertiary forms being undistinguishable from species which now 

 exist. 



The greater number of Mollusca are inhabitants of the sea, General 

 some passing their whole life at the surface hundreds or thousands t j 011< 

 of miles away from land ; others at the bottom of the ocean at all 

 depths, some having been dredged at five miles from the surface. 

 Many are found in much shallower water, and a large number 

 between tide-marks. Rivers and lakes furnish an immense variety 

 of forms, and vast numbers live on land in all situations — on 

 mountains, in valleys, forests, and deserts. 



Mollusks are either animal- or vegetable-feeders, the former 

 preying principally upon other members of their own class. 



The subjoined Table shows the systematic arrangement of the Syste- 

 Mollusca adopted in the Shell Gallery : — arrange- 



ment. 

 Class I. CEPHALOPODA. 



Subclass I. DIBRANCHIATA. Pages 



Order 1. Octopoda : Octopus or Poulp and Argonaut . . 9, 10 

 2. Decapoda : Squids and Cuttlefishes 10-12 



Subclass II. TETRABRANCHIATA. 



N.vuTiLiDiE : Pearly Nautilus 12, 13 



Class II. PTEROPODA. 



Order 1. Thecosomata : Cavolina, Cymbulia, Limacina. 13 



2. Gymnosomata : Clio, Euribia 14 



Class III. GASTROPODA. 



Subclass I. PROSOBRANCHIATA. 



Order 1. Pectinibranciiiata : Rock-Snails, Whelka, 

 Olives, Harp-shells, Cones, Stroinbs or Wing- 

 shells, Periwinkles, Carrier-shells, Sec 15 22 



2. Scutibranchlvta : JSWites, Top-shells, Ear- 



shells, and Limpets 22-25 



3. Polyplaoophora : Chitons 25-27 



