Geology . placed. The fauna retained, however,a general molluscan aspect. Both the bivalves and the univalvesgave proof of better adaptability to the vicissitudes of the coastaltracts than most other forms, and whether warm or cold waters pre-vailed, held their dominance. Figs. 457 and 458 show a few of thecharacteristic types. Compared with the Eocene group, Fig. 434, theresemblances will be found, by the untechnical observer, more strikingthan the differences. Notwithstanding the provincializing agencies, there were manyclose correspondences between the faunas of the western and the easterns
Geology . placed. The fauna retained, however,a general molluscan aspect. Both the bivalves and the univalvesgave proof of better adaptability to the vicissitudes of the coastaltracts than most other forms, and whether warm or cold waters pre-vailed, held their dominance. Figs. 457 and 458 show a few of thecharacteristic types. Compared with the Eocene group, Fig. 434, theresemblances will be found, by the untechnical observer, more strikingthan the differences. Notwithstanding the provincializing agencies, there were manyclose correspondences between the faunas of the western and the easternsides of the Atlantic, probably due partly to intermigration and partlyto parallel evolution. These correspondences have been set forth byDall in the following quotation:2 In a general comparison of the European and American Miocene we find, among other things which may be cited as parallelisms: in land vertebrates Papers previously cited. 2 Md. Geol. Surv., Miocene volume, 1904, pp. cli-cliii. 292 Fig. 457.—Miocene Pelecypods: a and b, Area (Scapharca) staminea Say; c and dCorbula idonea Conrad; e, Crass tellites marylandicus (Conrad); /, Phacoides (Pseu-domiltha) foremani (Conrad); g, Tellina (Angulus) prodncta Conrad; h, Leda con-centrica (Say); i, Modiolus dalli Glenn; j, Astarte thomasii Conrad; k, Ensis directus(Conrad); I, Spisula (Hemimactra) marylandica Dall; m, Isocardia markoei Conrad;n, Cardium (Cerastoderma) leptopleurum Conrad; o, Pecten (Chlamys) madisoniusSay; p, Venus ducatelli Conrad; q, Ostrea carolinensis Conrad. (After MarylandGeological Survey.) THE MIOCENE PERIOD. 293
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