BRACHIOPODA. 127 



specimens. The passage for tlio 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 growtli 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 IV 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. Barranue 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 B. nitida,t 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. ?, in 



* Systeme Siliirien ilu Centre de la Boheme, vol. v, pi. 97, tig', v, 1 A, 2 a. 

 t Systeme Siluiien du Centre de la Boheme, vol. v, pi. 100, fig-, ii. 

 I Permian and Carboniferous Supplement, pi. xxx, fig. 13 a. 



