THE ANNALS AND MAGAZINE OF NATURAL HISTORY. [FOURTH SERIES.] No. 34. OCTOBER 1870. XXVI.-The Ostracoda and Foraminifera of Tidal Rivers. By GEORGE STEWARDSON BIADY, C.M.Z.S., and DAVID ROBERTSON, F.G.S. With an Analysis and Descriptions of the Foraminmfera, by HENRY B. BRADY, F.L.S. [Plates XI. & XII.] Part II. THE Rhizopoda inhabiting brackish water are interesting alike in their zoological and physiological aspects. The marine species belonging to these lower types of animal life are well known so far as concerns the British seas, and their mutual relationships have been thoroughily studied; the freshwater fauna of corresponding organization has also received careful attention at the hands of able naturalists; but researches on the two subjects have been prosecuted in a great measure without reference to each other, and our knowledge of the intermediate fauna is consequently fragmentary and of limited value for purposes of comparison. The results detailed in the present paper have no caim to be regarded as an exhaustive treatment of the subject, but are offered rather as another instalment towards the history of an interesting phase of animal existence. The structure of the investment of the sarcode body of theRhizopoda, and its chemical and physical characters, havebeen regarded as forming the most reliable basis for classifi-cation; but how much the nature of the carapace dependsupon mere external circumstances has already been shown, withrespect to the Difflugian group, by Dr. Wallieh; and thereean be little doubt the same views are equally applicable toSome genera of the order Retieularia. Hence a few prelimi-nary remarks may not inaptly be devoted to general consider-Ann. & Mag. .f ist. Ser. 4. Vol.vi. 18
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