BRACHIOPODA. 
201 
The internal structure of these species has never been carefully elucidated, 
and it is a matter of great difficulty to obtain material suitably preserved for 
the elaboration of the critical features of the hinge. Clean internal casts are 
seldom found, and no instance of the silicification of the valves has come to 
our notice. By careful serial sectioning, however, it has been possible to ascer¬ 
tain with reasonable accuracy the character of the hinge. The teeth are 
usually supported by short vertical lamellae; the hinge-plate is quite small and 
is composed of two broad, short lateral processes, which are divided, for a por¬ 
tion of their length only, by a median incision extending to the bottom of the 
valve but not forming an inceptive spondylium as in Camarotoechia. The 
dental plates are large. There is but the barest indication of a median septum 
in the brachial valve. The muscular impressions are small and not deep; 
those of the pedicle-valve making an oval scar continued from the narrow ped¬ 
icle-cavity ; those of the brachial valve being narrow, elongate and extremely 
obscure.* The interior of the pedicle-valve frequently preserves the ovarian 
pittings and vascular sinuses while the characters are but faintly retained on 
the brachial valve. The development of these features seems to be of specific 
or varietal value only, as they are more rarely shown in the European examples 
of R. cuboides and are absent in R. Emmonsi, which is a more finely plicated 
shell, possessing other internal structure here described. 
The characters described are distinctive, but that they also occur in such 
allied species of the middle Devonian as R. procuboides, Kayser, R. primipilaris, 
von Buch, and R. parallelepipeda, Broun, we can only surmise from a similarity 
of exterior. They are reproduced with a very slight development of the median 
septum, in R. Grosvenori, Hall, of the St. Louis limestone. 
To shells of this nature may appropriately be applied the designation Hy- 
POTHYRis, King, 1846. There may seem to be some objection to the adoption 
of this term, which was introduced at an earlier date by Phillips! foi* certain 
* Davidson has given, on plate ii, of his Supplement to the Devonian Brachiopoda, figures (19, 19a) of 
an internal cast which is referred to R. cuboides, but it would seem to Le an erroneous reference. There is 
nothing in the figures which suggests this species, but it appears to represent a concavo-convex shell with 
an extended beak and strong flabellate muscular scars on both valves ; in many respects suggestive of a 
species of Eatonia. 
t Palaeozoic Fossils of Cornwall, Devon, and West Somerset, p. 35. • 1841. 
