GEOLOGICAL SUCCESSION OF GASTEROPODS. 499 



characteristic of the Primary rocks, Loxonema and Euomplialus range 

 through the Primary to the Trias, Holopea is Cambrian, Macrocheilus 

 is limited to the Devonian and Carboniferous rocks, Nerinoea ranges 

 from the Inferior Oolite to the Upper Chalk, Trocho- 

 toma extends from the Lias to the Coral Eag, Rimula ex- 

 tends from the Great Oolite to the Coral Rag. 



The existing genera which are known to commence in 

 the older Primary rocks are not very numerous ; the oldest 

 are Turbo, Chemnitzia, Patella, Chiton, and Pleurotomaria. 

 With the Devonian rocks Natica, Trochus, Dentalium, and 

 Phasianella begin. Calyptrea and Fissurella may date 

 from the Carboniferous, and Rissoa appears with the Permian strata. 

 With the Secondary strata Emarginula and Cerithium commence 

 in the Trias. The Lias contains the oldest known species of Ptero- 

 ceras, Aporrhais, Nerita, and Pileopsis. Fusus is first known from 

 the Bath Oolite, Scalaria from the Coral Rag, Melania, Paludina, and 

 Valvata are known first from the Wealden, Rostellaria, Pyrula, Tur- 

 ritella, and Vermetus from the Neocomian ; while the Chalk brings 

 in Strombus, Fasciolaria, Gancellaria, Dollum, Conus, Plurotoma, 

 Voluta, Mitra, Cyprcea, Phorus, and Hipponyx. In the Lower Ter- 



Fig. 130. Voluta 

 (Lower Tertiary type). 



Fig. 131. Voluta. 

 (Upper Tertiary type). 



tiary stratxi fossil species are met with of Seraphs, Murex, Typhis, 

 Ranella, Triton, Terebra, Nassa, Purpura, Cassis, Cassidaria, Oliva, 

 Ancittaria, Volvaria, Ovulum, Potamides, Melanopsis, Solarium, Neri- 

 tina, Crepidula. In the Middle Tertiary the genera Turbinella, 

 Haliotis, and Litorina are found for the first time. 1 



Cephalopoda. Cephalopoda include a large number of extinct 



1 Monographs of the British Tertiary Mollusca by Searles Wood have been 

 published by the Palaeontographical Society. 



