Brady— On Involutina Liassica. 195 
crystalline masses, giving no evidence of structural peculiarity. 
There are, however, some few transverse sections which present a 
series of ill-defined parallel lines running from the median line to the 
upper and lower surface; an appearance which has doubtless been 
associated with the ‘columnar’ structure of the Nummulite when the 
organism was supposed to belong to that group. 
ORC Ve 
Fig. 1. Diagram-outline of the horizontal section Fig. 2. Diagram-outline of the shell-wall 
of Involutina Liassica, showing how the infold- of Tnvolutina forming the septa by in- 
ings of the semi-tubular shell form the im- foldings. 
perfect septa. 
One of the most important characters in the true Nummulite 
(Nummulina) is the mode in which the chambers are prolonged 
laterally into two alar processes, which completely embrace the 
row lying immediately within them; we also find in the various 
members of the group evidences of a higher type of organization 
in the system of canals which traverse the shell-substance. It 
will be seen that these peculiarities are entirely wanting in the 
specimens before us. 
There seems little difficulty in placing the Foraminifer in 
question in Dr. Carpenter’s family Zitwolide; and in its struc- 
ture and mode of growth it has obvious affinities to the genus 
Trochammina, P. & J., falling into its place most naturally 
between the lower Rotaline and the sandy free-growing Tro- 
chammina squamata, P. & J. We constantly notice in Forami- 
nifera a tendency in some of the members of a group, especially 
the lowermembers, to simulate in appearance those of correspond- 
ing development in other and distinct groups. ‘The result is 
that varietal forms have often a greater general resemblance to 
varieties of genera from which they are far removed than to their 
own immediate congeners. In this way Jnvolutina liassica may 
be regarded as an isomorph of Pulvinulina vermiculata in its 
exogenous deposit. This latter peculiarity, which, as far as I 
have been able to observe, is invariably present to a greater or 
less extent, is sufficiently characteristic to distinguish it from 
Trochammina, the genus to which I have said it has nearest 
affinity. 
I will now refer to M. Terquem’s second paper on the ‘ Fora- 
minifera of the Middle and Lower Lias’ (Mém. de l’Acad. Imp. 
de Metz, 1860-1861), in which two species of Foraminifera are 
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