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CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



for the " passage forms between Tr. gordialis and Tr. incerta in one direction and Tr. 

 pusilla in the other." The figures (PI. Ill, figs. 11 — 15) are reproduced, with the 

 assistance of specimens kindly lent by Mr. Kirkby, from the drawings accompanying 

 Messrs. Jones, Parker, and Kirkby's paper. 



Distribution. — Permian only : — occurs with the allied Trochammina in the Lower and 

 Middle Magnesian Limestones of the North of England. 



Troohammina Robertsoni, nov. PI. Ill, figs. 6, 7. 



Characters. — Test free, oblong, compressed ; composed of a spuriously septate tube 

 reflexed or doubled on itself more or less regularly in a manner analogous to the Quin- 

 queloculine Miliolce. Aperture relatively large, rounded or arcuate. Test, exceedingly 

 thin and delicate; texture very finely arenaceous. Length j^oth inch (0 21 mm). 



For specimens of this exceedingly minute and delicate form I am indebted to my 

 friend Mr. David Robertson, F.G.S., of Glasgow, who discovered it in some of the 

 Carboniferous shales of the West of Scotland, and whose name therefore may very pro- 

 perly be associated with it. The specimens were at first assigned to Tr. pusilla, in the 

 belief that their very small size, more regular structure, and delicate texture, were the result 

 merely of different external conditions of life ; but I have hitherto found no intermediate 

 forms to justify this conclusion, and have therefore given to it a distinctive name. The 

 resemblance of the specimens to minute Quinqueloculino; is remarkable, not merely in 

 the general form and manner of growth, but in the constriction of the tubular body 

 near the ends of the test (especially noticeable in the outermost convolution) which 

 imparts an appearance almost precisely like the segmentation of a true Miliola. It is 

 scarcely necessary to dwell on the superficial nature of this resemblance. The non- 

 porcellanous texture of the test is sufficient to separate the organism from its white- 

 shelled isomorphs, whilst its cemented, finely arenaceous structure links it as clearly to 

 the genus Trochammina. 



Distribution. — Trochammina Robertsoni has only hitherto been found in beds of the 

 Upper Carboniferous Limestone Group of Scotland. It may, however, have a wider 

 range than we know of, for, from its very minute size and inconspicuous appearance, it 

 may be easily overlooked in searching the dull-coloured material yielded by Carboniferous 

 rocks. 



