Orbitolites Mantelli, Cart.^from Burma. 343 



vertically in the centre, from which point it gradually and 

 uniformly diminishes to the thinness of a wafer at the cir- 

 cumference. Layers of compressed cells on each side of the 

 central plane, amounting in the centre of a vertical section to 

 about sixteen, diminishing in this respect towards the cir- 

 cumference, presenting in the horizontal section the same 

 cells under a circular or hexagonal form, in juxtaposition but 

 for the intervention of a thin line of translucent shell-sub- 

 stance, through which, in specimens infiltrated with red or 

 yellow oxide of iron, the intercellular canals of communica- 

 tion, by their opaque yellow colour, may be seen to pass, but 

 no columns of the opaque white, shelly substance which 

 especially characterize this structure in Orhitoides dispansa. 

 These layers of vertically compressed cells present, in the 

 horizontal planes, a similar arrangement to the centrifugal 

 lines of an engine-turned watch-case, and are covered in on 

 both sides by a very thin superficial or terminal layer, in which 

 the cells markedly differ from those of the subjacent planes 

 in the irregularity of their outline and their variability in size, 

 although^ under the microscope, they also may be seen to be 

 separated by the thin line of intercellular translucent shell- 

 substance, like that which, in the infiltrated specimens, is 

 traversed by the canals of intercellular communication as in 

 those of Orhitoides dispansa^ but none of the " conical 

 columns of non-tubular substance " of the late Dr. Carpenter 

 (' Introduction to the Study of the Foraminifera,' p. 302), that 

 is, of our opaque white, shelly substance which so essentially 

 distinguishes this species from Orbitolites Mantelli^ Cart., as 

 before mentioned. General appearance of the " hand-speci- 

 mens " under examination, which indicates that of the stratum 

 from which they were taken, sandy ; the matrix consisting of 

 a combination of microscopic grains of quartz and a small 

 quantity of argil together with a considerable portion of 

 microscopic Foraminifera, in the proportion of 2 of the former 

 to 1 of the latter, in which the specimens of Orbitolites Man- 

 telli^ var. Theobaldi^ which are composed of apparently 

 homogeneous, semitranslucent calcite, in a compact or crystal- 

 line state, lie, like a collection of large leaves, thus contrasting 

 forcibly in their homogeneity and general appearance with 

 the gritty character of the matrix. Colour of the matrix grey 

 when fresh, rusty brown after exposure, tough, breaking with 

 a rough fracture ; structure laminar from the presence of the 

 leaf-like fossils. Microscopic Foraminifera consisting chiefly 

 of Discoids and Textularice. Although the hand-specimens, 

 which altogether present about 150 square inches of surface, 

 were carefully examined all over with a strong lens, I could 



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