Bracuiopopa. 905 
and divaricator muscles, and probably rests upon the bottom of 
the valve and is not vaulted. 
In the brachial valve there is a prominent cardinal process 
from the base of which diverge two lateral ridge or socket walls, _ 
lying just within the hinge-line; behind them are linear depres- 
sions or dental sockets. Thereis also a low median ridge extend- 
ing from the base of the cardinal process into the pallial region. 
- The substance of the shell shows a coarsely prismatic cellular 
structure, as in Poramsonires and Eicnwarpia. According to 
Barrors, this cellular lamina is not superficial but is covered by 
a thin epidermal layer. 
Type, Aulcoryhynchus Pachti, Dittmar. Carboniferous limestone. 
‘Distribution. Carboniferous. 
Richthofenia, Kayser. 1881. 
These peculiar fossils, which bear a striking external resem- 
blance to certain operculated corals, and present some suggestive 
Fia. 667. Fie. 689, 
Richthofenia Lawrenciana, de Koninck. 
Fia. 666, The exterior of the two valves in articulation. 
Fia 687. Longitudinal section of the pedicle-valve; showing the interior cavity and the cellular 
shell substance. 
Fie. 668. The interior of the pedicle-valve; showing the hinge-line and muscular scars. 
Fig. 669. The interior of the brachial valve. CWaAAGEN.) 
similarities to the lamellibranchs Hirrurrres and Raptorrrss, 
have been carefully elaborated by Waacun, who arrives at the 
114 157 
