﻿VALVULINA. 



87 



Valvulina Youngi, var. contraria, Brady. PI. IV, figs. 7, a, b. 



Valvulina Youngi, var. contraria, Brady, 1873. Mem. Geol. Survey Scotland; 



Expl. Sheet 23, pp. 63, 95, &c. 



This form bears exactly the same relation to Valvulina Youngi that V. palceotrochus, 

 var. compressa, bears to its type ; that is to say, instead of being shaped like a cone with 

 a circular base, its transverse section is of a long oval form. The chambers are sub- 

 divided into chamberlets just as in V. Youngi ; in other respects the divergence from 

 the parent form is in precisely the same characters as detailed in the description of 

 V. compressa, and for similar reasons a varietal name has been provisionally assigned to 

 it. Both the circular and oval forms of V. Youngi are rare, but the number of specimens 

 of the latter variety is sometimes larger than that of the form which has been regarded 

 by analogy as its type, differing in this respect from the corresponding modification of 

 V. palceotrochus. 



Distribution. — Much the same as that of Valvulina Youngi ; indeed, no very great care 

 has been used to keep the record of the two distinct. 



Valvulina decurrens, Brady, PI. Ill, figs. 17, 18. 



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



pp. 63, 95, &c. 



Characters. — Test free or adherent, spiral, complanate ; in the form of an outspread, 

 much depressed cone, with circular base and thin, sharp, often irregular margin. Spiral 

 band usually distinct ; septation very obscure, partial, or often entirely abortive. Diameter, 

 -^g- inch (about l - mm.) or more. 



The outspread forms, of which Valvulina decurrens is the representative, stand in 

 somewhat the same relation to V. palaotroc/ius as that which Trochammina incerta bears 

 to the regularly septate type of its own group. In neither genus can any hard line of 

 demarcation be drawn between the successive " species." 



Valvulina decurrens is a thin, complanate variety, often a mere scale-like disc, com- 

 monly much thinner than appears in fig. 17, b, which, owing to the upturned edge of the 

 specimen, has a greater apparent solidity than is usually seen in characteristic examples. 

 Sometimes its spiral structure is obscured, as in this figure, by confused, oblique septation, 



