﻿88 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



but frequently, especially in weathered specimens, the whole course of the spiral band, 

 unbroken and unsegmented, may be traced on the upper surface of the test, as in fig. 18. 



The diameter of the shell is at least as great as that of V. palaotrochus, often greater; 

 the height of the cone sometimes not more than -^q inch (0'13 mm.) at the centre. 

 The lower surface is usually flat and irregular, depending somewhat on the nature of the 

 body to which it has been adherent during life. It is seldom possible to detect the 

 aperture. 



Distribution. — In the Lower Limestones of England, rare ; in the Yoredale rocks 

 much commoner. In Scotland found in the Calciferous Sandstones, and in the Lower 

 and Upper Carboniferous Limestone Groups. It appears in the Lower Limestones of 

 the North of Ireland and in the Upper Coal-measures of North America. Not a 

 Permian species. 



Valvulina plicata, Brady, PI. IV, figs. 10, 11. 



Valvulina plicata, Brady, 1873. Mem. Geol. Survey Scotland ; Expl. Sheet 23, 



pp. 66, 95, &c. 



Characters. — Test free or adherent, spiral, quasi-rotalian consisting of about four 

 convolutions ; upper surface convex ; lower surface flat or very slightly concave ; margin 

 rounded. Chambers numerous, more or less inflated, often irregular in size ; septa 

 oblique, curved, marked by slight depressions on the exterior. Diameter, yq inch 

 (0'5 mm.) or less. 



The term " spiral " as applied to the arrangment of the segments of any of the 

 Valvulina is not to be read in quite the same sense as in the higher groups of Forami- 

 nifera like the true Rotalians. Specimens of Valvulina plicata are occasionally met with, 

 like PI. IV, fig. 11, so neat and regular in appearance that they might easily be mis- 

 taken for small Discorbina, but these are exceptional. Much more frequently it is 

 impossible to trace any consecutive spiral series, and instead of a band of uniform and 

 well-separated segments coiled regularly on itself, the effect is more like that of an 

 oval tube twisted at intervals and so irregularly disposed that the order of the chambers 

 may be a matter of doubt. Something of the obscurity may be attributable to the age 

 of the fossils and the changes produced by the process of mineralization. In localities 

 where the species is common there is generally a residuum of fairly marked examples, 

 like figs. 10, a — c, possessing what may be looked upon as average characters, and upon 

 such specimens its claim to a distinctive name is based. 



Valvulina plicata is very closely related to V. palaotrochus, but its depressed, 

 rounded, convex (rather than conical) shape, its plicate septation, smaller size and 



