134 



MANUAL OF THE MOLLUSCA. 



nay, often seemingly producing results opposed to a priori 

 probability, and at variance with the suitableness of con- 

 ditions?* 



Tbe 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 

 mollusca will 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. 



Argonautidee 4 2 



OctopodidcB 63 — 



Teuthidae .• 104 31 



Belemnitidse — 140 



Sepiadse .". 30 16 



Spinilidae 3 — 



204 189 

 Tetrahranchiata. 



Nantilidae 6> . 



Orthoceratidse —\ 



Ammonitidffi — 1600 



6 2193 

 Uasteropoua. Prosohrnnchiata. 



Strombidaet 87 393 



Muricidse 993 703 



Buccinidas 1,144 352 



Conidee 856 462 



Volutidffi 686 210 



CypraeidsB 227 97 



Naticidee 268 340 



Pj'raraidellidBe 216 394 



Cerithiadse 192 610 



Melaniadae 424 60 



TurriteUidae: 320 290 



Littorinidae 410 220 



Paludinidse 217 110 



CalyptrEcidse 160 101 



Turbinidse 855 906 



Haliotidae 104 136 



Fissiirellidee 201 76 



Eecent. Fossil. 



Neritidffi 428 103 



Patellidte 368 104 



Dentaliadse 60 125 



Chitonidee 250 37 



8,-165 5,819 

 Pulmonifera. 



Helicidse 4750 316 



Limacidge 93 4 



Limnreidge 332 185 



(Mi.rine) 193 37 



(Ditto, shell-less) 36 — 



5,404 542 

 Operculatcd Pulmonifera. 



Cj'clostomidee 903 45 



Aciculidse 28 1 



931 46 

 Tccti-hranchinta. 



Tornatellidse 62 166 



Bullidae 168 88 



Aplysiadse 84 4 



Pleurobrancliidse 28 5 



PhylUdiadce 14 — 



356 263 

 Nudihranchiata . 



Doridse ., 160 — 



Tritoniadse 38 — 



;i:olid8e 101 — 



rhyllirhoidoe 6 — 



Elysiudte 13 — 



318 



■■ Burcliell, in Darwlu's Journal, p. 87. 



t Including Aporrhciis 



X With Scalaria. 



