74 CARBONIFEROUS AND PERMIAN FORAMINIEERA. 



Cornuspira, based upon a " test, calcareous, porcellanous, and compact," on the ground 

 that \vith a magnifying power of eighty diameters he is able to demonstrate in a large 

 number of specimens the existence of a multiplicity of pores. Supposing this to be the 

 case, the specimens would be assigned by rhizopodists generally to the genus Spirillina, 

 not to Cornuspira. The rigorous examination of the set of specimens M. Terquem has 

 been good enough to furnish, with powers varying from twenty diameters to six hundred 

 or more, has not enabled me to detect pores in the shell-wall in a single instance. Lest 

 I should have been unconsciously influenced by familiarity with similar organisms, the 

 " imperforate" character of which has never been questioned, the specimens were sub- 

 mitted to a friend of great experience in the use of high magnifying powers, though in 

 investigations of another order, and his reply was decisive that no perforations existed, 

 that any appearance as of pores was caused by mere superficial rugosity or by minute 

 tubercles, and that the illusion by which they appeared like pores was readily dispelled by 

 varying the method of illumination. It should, however, be remarked, that the Mesozoic 

 specimens are very minute, and the structural characters are much more obscure and 

 difficult of determination than in individuals of larger dimensions. I must add that it is 

 with great deference to the views of so assiduous a student of fossil Microzoa as M. 

 Terquem that I give expression to conclusions differing from his on a somewhat important 

 point. 



Distribution. Trochammina incerta is one of the most abundant of Palaeozoic 

 Foramim'fera. It is found throughout the Carboniferous Limestones of England, and in 

 the Lower and Upper Groups of Scotland. I have note also of its occurrence in the 

 Fusulina rocks of the Caucasus. 



In the Permian beds specimens are common, and often attain very fine dimensions. 

 It is found in the Lower and Middle Magnesian Limestones of England, and in the 

 Zechstein proper of Germany. 



TROCHAMMINA CENTRIFUGA, Brady. PI. II, figs. 15 20. 



INVOLUTINA INCEHTA, Brady, 1869. Report Brit. Assoc., Exeter Meeting, p. 382. 

 TROCHAMMINA CENTEIFUGA, Brady, 1873. Mem. Geol. Survey Scotland, Expl. Sheet 



23, p. 95. 



Id., 18/3. (In Young and Armstrong's Catal.) Trans. 

 Geol. Soc. Glasgow, vol. iv, p. 271. 



Characters. Test depressed, thin, piano-spiral ; formed of a tube of uneven 

 diameter, convoluted in its earlier, rectilinear in its later stages of growth. Aperture ter- 

 minal, round, usually unconstricted. Length about -^th inch (0'5 mm.) ; diameter of 

 spiral portion about inhyth inch (0'25 mm.). 



