BRACHIOPODA. 
127 
specimens. The passage for the pedicle is so oblique to the planes of the sur¬ 
faces of the valve that its inner termination is not abrupt but commonly pro¬ 
duced into a fine groove, visible over nearly or fully the distal half the length 
of the pedicle-area and sometimes traceable even to the margin of the shell. 
Contemporaneous with the growth of the shell is the development of a callosity 
close about the margins of this groove, which often becomes so high as not only 
to have deepened the passage, but in advanced age to have wholly enveloped it, 
the two callosities becoming coalesced and leaving an opening for the pedicle 
only at their posterior extremity. (See Plate IY f, figs. 8-17.) This callosity 
is developed with substantial symmetry in D. Herzeri (see foot-note on preced¬ 
ing page), D. marginalis , D. ampla, etc., occasionally showing a tendency to 
irregular, though not unsymmetrical growth. In many species it never attains 
a great development, being scarcely more than a linear elevation or a narrow 
ridge, bordering and partially or wholly enveloping the pedicle-groove ; the 
adult condition in such species being essentially identical in this respect to the 
earlier stages of growth in those where the callosity eventually closes all but the 
aperture of the foramen. In Orbiculoidea tenuilamellata , we find the internal 
character of the pedicle-area of precisely the same nature. On the inside no 
indication is given of the length of the external groove, but the inner callosity 
extends from the apex almost, if not, in some instances, quite to the posterior 
margin, without leaving any trace upon the external .surface, when the shell 
is uncompressed. 
So far as we are aware the features described above have been rarely illus¬ 
trated by any author. Barrande has given* illustrations of the exterior and 
interior of his species, D. Bohemica, the former showing the short external groove, 
and the latter the inner prolongation of the groove or ridge to the margin. 
The same features may be seen in his figures of D. Mceotis.f Attention may 
also be directed to Mr. Davidson’s figure of D. nitida,\ which shows very 
distinctly from the interior the floor of the long pedicle-groove and the inner 
opening of the foramen; and to Mr. Meek’s figure of Orbiculoidea , sp. I, in 
* Syst&me Silurien du Centre de la Boheme, vol. v, pi. 97, fig-, v, 1 A, 2 a. 
t Systeme Silurien da Centre de la Boheme, vol. v, pi. 100, fig. ii. 
J Permian and Carboniferous Supplement, pi. xxx, fig. 13 a. 
