Reid, C.—The Pliocene Deposits of Britain, "Mem. Geol. Survey of the United Kingdom," 1890.

Rütimeyer, L.—"Die Herkunft unserer Thierwelt," 1867.

Sars, G. O.—Crustacea Caspica, "Bull. Acad. Imp. d. Sciences St. Petersburg," vol. xiii., 1893-94.

Scharff, R. F.—a. On the Origin of the European Fauna, "Proc. Royal Irish Acad." (3rd. ser.), vol. iv., 1897. b. Some Remarks on the Distribution of British Land and Freshwater Mollusca, "Conchologist," vol. ii., 1893. c. Étude sur les mammifères de la Région Holarctique, "Mém. de la Soc. Zool. de France," vol. viii., 1894.

Schulz, A.—"Grundzüge einer Entwicklungsgeschichte d. Pflanzenwelt Mittel-europas," 1894.

Sharpe, R. Bowdler.—British Museum Catalogue (Birds).

Simroth, H.—Eine Bearbeitung d. Russischen Nacktschnecken fauna, "Ann. Musée Zool. St. Petersburg," 1896.

Sjögren, H.—Ueber das diluviale Aralo-Kaspische Meer und die nord-europäische Vereisung, "Jahrb. d. Kais. K. Geol. Reichsanstalt," vol. xl., 1890.

Sollas, W. J.—On the Origin of Freshwater Faunas, "Trans. Royal Dublin Soc." (2nd ser.), vol. iii., 1884.

Speyer, A. and A.—"Die Geographische Verbreitung der Schmetterlinge Deutschlands und der Schweiz," vol. i., 1858.