CONTRIBUTIONS TO PALEONTOLOGY. 317 



The interior of the dorsal valve, fig. 5, shows a narrow longitudinal 

 septum s, which, beginning at the apex, reaches nearly to the base of the 

 shell. The great elevation of this septum is shown in figure 7. There 

 is a very slender cardinal process, J, beneath the apex of the beak, and 

 long narrow grooves or teeth-sockets, b, b. In the ventral valve, fig. 6, 

 the margins, at some distance below the apex, are convex or elevated 

 and attenuate, resting in the long 

 narrow groove in the margin of the 

 opposite valve. So far as observed, 

 there are no distinct dental lamelte, 

 the margins of the valve performing 

 ^''^•i.iMi*** that function, and serving as fulcra in 



the opening and closing of the valves. There is no evidence of a longi- 

 tudinal septum in the ventral valves of two species of the Niagara age ; 

 but there is a transverse septum or diaphragm extending across the base 

 of the rostral cavity, and continuing to the apex of the shell. Below 

 this diaphragm, and between it and the outer shell, there is a narrow 

 space or slit which extends to the apex of the shell. This diaphragm, 

 or interior shell, is smooth and solid, extending to and forming the 

 smooth umbo and acute apex of the valves, beneath which is a false 

 area, as shown in the figure. 



The character of the dorsal septum is better shown in fig. 7, which is 

 a longitudinal section of the two valves. The apex of the ventral valve 

 is very narrow and pointed ; the close solid shell of the diaphragm is 

 apparently folded back to form the false area d, and there does not 

 usually appear any evidence of a foramen at the apex. There is evi- 

 dently a continuous space between the diaphragm c, and the shell c' as 

 shown in the figure ; and this separation extends along the central portion 

 at least for the width of the sinus, and, continuing towards the beak, has 

 given the denuded apex, which sometimes has the aspect of a partially 

 closed foramen/. It seems scarcely in accordance with the usual struc- 

 ture of the Brachiopoda, that the pedicel should pass through the narrow 

 slit between the diaphragm and the outer shell, entirely outside of the 

 rostral cavity ; still this space has evidently served the animal for com- 

 munication with the exterior. We have some analogy to this condition 

 in the Genus Siphonotreta, and I have supposed that the diaphragm 

 may represent a modification of the dental lamellae. The muscular 

 impressions are just below the margin of the diaphragm. 



