502 MOLLUSCA SUB-KINGDOM vi 



vicarious. A very different aspect is presented by the Eocene fauna of 

 Australia, New Zealand, and South America, where we find the evident fore- 

 runners of forms now inhabiting the southern portions of the Atlantic and 

 Pacific Oceans. 



Still more intimate is the relationship existing between the fossil land and 

 fresh-water Gastropods and their descendants on the several continents. It 

 has been observed that Miocene faunas bear a decidedly tropical stamp. On 

 this account European and American forms from the inland Miocene deposits 

 bear some resemblance to the recent faunas of the Azores and the West 

 Indies, as well as to the land and fresh- water Gastropods inhabiting the colder 

 latitudes of Europe and Asia. Only as recently as the Pliocene did each 

 geographical province come to assume its present distinctive features. 



In general, the stratigraphic sequence of Gastropod groups corresponds 

 closely with the zoological order, the most generalised forms appearing first, 

 the more specialised later. Beginning with the two-gilled PMpidoglossa and 

 the Docoglossa, followed by the single-gilled Pihipidoglossa, Opisthobranchs, and 

 taenioglossate Ctenobranchs, the series leads to Racliiglossa in the later Mesozoic, 

 and culminates in the great increase of rachiglossate and toxoglossate families 

 in Tertiary and Recent times. 1 (See tables, pp. 500, 501.) 



^ CEPHALOPODA. 2 



Head sharply defined in recent forms, except Nautilus. Foot transformed into a 



[ l Grateful acknowledgments are due to Professor Henry A. Pilsbry, of the Philadelphia Academy 

 of Natural Sciences, for his revision of the preceding Gastropod chapter. The difficulty of 

 adapting a strictly zoological classification, based largely upon the anatomy of the soft parts, to the 

 practical needs of the palaeontologist, is strikingly illustrated by the class of Gastropods. A 

 revolutionary, or even extreme course has been avoided ; and it is hoped that the system herein 

 adopted will be found to possess some practical advantages. TRANS.] 



2 Literature : 



Angdin, JV. P., Fragmenta Silurica, edited by G. Lindstrom. Stockholm, 1880. Arthaber, 

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 und Orients, Mojs. und Neumayr, Bd. X. Hefte I.-IV.), 1896. Barrande, J., Systeme Silurien de la 

 Boheme, vol. II. Cephalopodes. 1867-77. Bayle, JE., and Zeiller, R., Explication de la Carte geolo- 

 gique de la France, vol. IV., Atlas. Paris, 1878. Beecher, G. E., On the Development of the Shell 

 in Tornoceras (Amer. Journ. Sci. [3], vol. XL. p. 71), 1890. Beyrich, II. E., De Goniatitis in monti- 

 bus rhenanis occurrentibus. Inaug. Dissert. Berlin, 1837. Billings, E., Palaeozoic Fossils. Geol. 

 Surv. Canada, 1865Blainville, H. M. de, Memoire sur les Belemnites. Paris, 1827. Blake, 

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Canavari, M., Sui fossili del Lias inferiore nell' Appenino ceutrale (Atti Soc. Toscano, vol. IV. 

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 (Mem. Com. Geol. St. Petersb., vol. XIV. No. 3), 1895. Douville, H., Sur quelques fossiles de la 

 zone a Ammonites Sowerbyi (Bull. Soc. Geol. France [3], vol. XIII. p. 12), 1884-85. Sur la classi- 



