On the For ami nif era of the River Dee. 37 



VI. — On the Foraminifera of the River Dee. 

 By J. D. SiDDALL. 



The Microzoa inhabiting brackish water have formed the 

 subject of much careful study — the Ostracoda especially at 

 the hands of Mr. G. S. Brady and Mr. Robertson, the Fora- 

 minifera at those of Mr. H. B. Brady and the latter gentleman. 

 The interest which attaches to an intermediate fauna depends 

 very greatly on the completeness of its ascertained facts even 

 to minute particulars ; and it is with this view that the fol- 

 lowing paper is offered as a contribution to the general store 

 of knowledge. As the observations of which it is the record 

 refer entirely to the Foraminifera, it may be well at the outset 

 to note what has already been done in connexion with the 

 subject. 



In his Catalogue of the Foraminifera of the north-eastern 

 portion of the English coast*, Mr. H. B. Brady draws atten- 

 tion to the Rhizopoda inhabiting the brackish pools of one or 

 two river-estuaries, commenting on the apparent alteration in 

 the material of the test in some well-known species as depen- 

 dent on their altered external conditions of life. 



The subject was resumed and entered upon at much greater 

 length by the same author in a paper which appeared in the 

 'Annals ' for October ISTOf. This memoir is founded on the 

 examination of material collected from upwards of thirty 

 localities, principally river-estuaries, round Great Britain. 

 In the preliminary observations the question of tlie chemical 

 and physical characters of the test is furtlier dwelt upon, and 

 tlie general conclusion drawn that in proportion to the decreased 

 salinity of the water the investment of the testaceous Rhizo- 

 poda becomes less and less calcareous, till at last in certain 

 species, which tolerate this process of dilution better than 

 others, the test ceases to be calcareous at all, and consists only of 

 a thin, brown, chitinous membrane, which is not dissolved by 

 either acids or alkalies. The species in which these phenomena 

 were esi)ecially noticed were Trochammina macrescens and 

 Quinqueloculina fusca^ the origin of both of which could be 

 traced to well-known marine forms. The sarcode, in like 

 manner, was shown often to acquire a green colour in brackish 

 specimens, apparently from the formation of chlorophyl. 



* " Catalogue of the Recent Foraminifera of Northumberland and 

 Durham," Nat.-Ilist. Trans. North. & Durliam (180(5), vol. i. p. 8(5. 



t " Tho Ostracoda and Foraminifera of Tidal Rivers," by Geo. S. 

 Brady, C.M.Z.S., and David Robertson, F.CI.S. ; with an Analysis and 

 Descriptions of the Foraminifera by Henry V>. Brady, F.L.8. (Part II.) 

 Ann. & Mag. Nat. Hist. eer. 4, vol.'vi. pp. 273-30G, pis. xi. & xii. 



