﻿86 CARBONIFEROUS AND PERMIAN EORAMINIEERA. 



Valvulina Youngi, Brady. PL IV, figs. 6, 8, 9. 



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



pp. 63, 95, &c. 



Characters. — Test free or adherent, obscurely spiral, trochoid ; composed of several 

 convolutions, of which the constituent chambers are all more or less visible on the 

 exterior. Inferior surface concave, and more or less irregular. Chambers subdivided 

 into one or more rows of chamberlets. Diameter, ^ inch (0 - 64 mm.) or more. 



In external configuration Valvulina Youngi closely resembles V. palteotrochus, for, 

 although the sub-division of the chamber-cavities by secondary septa may usually be 

 detected by markings on the exterior of the test, these structures are not of a nature to 

 affect its general appearance or contour. The two species are indeed very closely allied. 

 A glance at the figures of their respective transverse and perpendicular sections (PI. IV, 

 figs. 3, 4, and 8, 9) will show wherein the difference really lies. In some of the Car- 

 boniferous Foraminifera yet to be described the shelly ingrowths appear as though they 

 might have a tubular character ; but in the present case there can be little doubt, judging 

 from the transverse section (fig. 9), that they are true secondary septa, formed of more or 

 less continuous plates of shell-substance dividing the chambers into chamberlets. It will 

 be seen that the shell-wall and the primary septa are much thinner in V. Youngi than in 

 the forms with simple chambers, the secondary growths therefore probably serve to give the 

 necessary strength and solidity to the test. The same sort of provision, but on a much 

 more extended plan, is to be observed in some of the more complex arenaceous types of 

 Foraminifera, notably in Loftusia. 



I have much pleasure in associating with so interesting a form the name of one of the 

 earliest students of British Carboniferous microzoa, my friend Mr. John Young of Glasgow. 

 It was in his collection from the rich Brockley shale, that I first made acquaintance with 

 the species. 



Distribution. — In England only noticed hitherto at one locality in the Lower Lime- 

 stone Series, viz. Fallowlees, Northumberland. In Scotland at several localities per- 

 taining to the Lower Carboniferous Limestone Group, but not in any other portion of the 

 Series. In all cases very rare. 



