134 



MANTTAL OF THE MOLLTJSCA 



nay, often seemingly producing results opposed to a ^jriori 

 probability, and at yariance mtb the suitableness of con- 

 ditions ?* 



The answer is, that each fauna bears, above all things, the 

 impress of the age to which it belongs. Each has undergone a 

 series of vicissitudes up to the time when its barriers became 

 fixed, and after its isolation it has known no further change, 

 but decline. 



The number of living and fossil species of each, genus of 

 molluscawill be stated in the following pages, so far as they can 

 be ascertained. With some modifications, these numbers give the 

 following totals, by which the relative numerical development 

 of the orders and families will be seen. 



Eecent. Fossil. 

 Cephalopoda. Dibranchiata. 



Argonautidae 4 2 



Octopodidte 63 — 



Teuthidee 104 31 



Belemnitidse — 140 



Sepiadse 30 16 



Spirulidae 3 — 



204 189 

 Tdrahranchuita. 



Nautilidae 6) .„ 



Orthoceratidae — ) 



Ammonitidae — 1600 



6 2193 

 Gasteropoda. Prosobranchiata. 



Strombidset 87 393 



Mmicide 993 703 



Buccinidaj 1,144 352 



Conidae 856 462 



Volutidse 686 210 



Cji^raeidae 227 97 



Naticidze 263 340 



PjTamidellidae 216 394 



Ceiitliiadge 192 610 



Melaniadae 424 50 



TuiTiteUidseJ 329 290 



Littorinidse 410 220 



Paludinidae 217 HO 



Calyptreeidse 160 101 



Turbinidae 855 906 



Haliotidae 104 136 



Fissurellidae 201 76 



Recent. 



Neritidse 428 



Patellidse 368 



Dentaliadse 50 



Chitonidse 2-50 



8,465 

 Pulmonifera. 



Helicidse 4750 



Limacidae 93 



Limnaeidse 332 



(Murine) 193 



(Ditto, shell-less) 36 



5,404 

 Operculated Pulmonifera. 



Cyclostonaidse 903 



Aciculidae 28 



931 

 Tecti-branckiata. 



Tornatellidse 62 



Bullidse 168 



Aplysiadse 84 



Pleurobranchidse 28 



Phyllidiadce 14 



356 

 Nudibranchiata. 



Doridae 160 



Tritoniadse 38 



^olidae 101 



Phyllirhoidae 6 



Elysiadae 13 



318 



Fossil. 



103 



104 



125 



37 



5,819 



316 



4 



185 



37 



542 



45 

 1 



46 



166 



88 



4 



5 



263 



* Burchell, in Darwin's Journal, p. 87. 



I Including Aporrhais 



X With iScalaria. 



