DEVELOPMENT OF FAMILIES, ETC., IN TIME. 



245 



'' 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. The following table of the relative numerical 

 development of the orders and families, is taken from Wood- 

 ward and shows the extent of conchological knowledge twenty- 

 five years ago : — 





Kecent. 



Fossil. 





Recent. 



Fossil. 



Cephalopoda. Dibranchiata. 



JPatellidae, . . . 



368 



104 



Argonautidas, 



4 



2 



Dentaliadse, . . 



50 



125 



Octopodidse, . 



. 63 



— 



Chitonid^, . . 



250 



37 



Teuthidffi, . . 



. 104 



31 









Belemnitidse, . 



— 



140 





8465 



5819 



Sepiadse, . . 



. 30 



16 



rulmonifera. 







Spirulidse, . . 



3 





Helicidae, . . . 



4^50 



316 









Limacidae, . . . 



93 



4 





204 



189 



Limnseidse, . . 



332 



185 



Tetrahran 



chiata. 





(Marine), . . . 



193 



37 



Nautilidse, . . 



■ 6] 



593 



(Ditto, shell-less) 



36 



— 



Orthoceratidae, 



. — ; 









Ammonitidfe, 





1600 





5404 



542 



Gastropoda. Pr 

 Strombidse, 

 Muricidae, . 

 Buccinidse, 

 Conidse, 

 Volutidse, . 

 Cypraeidge, 

 Naticidse, . 

 Pyramidellidse 

 Cerithiadse, 

 Melaniadse, 

 Turritellidae, 

 LittorinidiK, 

 Paludinidge, 

 Calyptrseidffi 

 Turbinidge, 

 Haliotidse, . 

 Fissurellidse, 

 Neritidffi, . 



6 2193 

 )Sobran.chiata. 

 87 393 

 993 

 1144 

 856 

 686 

 227 

 268 

 216 

 192 

 424 

 329 

 410 

 217 

 160 

 855 

 104 

 201 

 428 



Operculated Puhnonifei'a. 

 C3'clostomid8e, . 903 45 

 Aciculidse, ... 28 1 



703 

 352 

 462 

 210 



97' 

 340 

 394 

 610 



50 

 290 

 220 

 110 

 101' 

 906 

 136 i 



76 

 103 



931 

 Tectibranchiata. 

 Tornatellidae, . . 62 

 Bullidse, ... 168 

 Aplysiadae, . . 84 

 Pleurobranchidse, 28 

 Phyllidiadse, . . 14 



356 

 Nu dibra n chiata. 



46 



166 



88 



4 



5 



263 



Doridffi, . . 

 Tritoniadae, 

 ^olidae, 

 Phyllirhoidfe, 

 Elysiadai, . 



160 

 38 



101 



6 



13 



318 



