276 



TWENTIETH REPORT ON THE STATE CABINET. 



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 lamellae, the margins 

 of the valve performing that function, and serving as fulcra in the opening 

 and closing of the valves. There is no evidence of a longitudinal 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. 



Fig. 5. Fig. 6. 



I ElCHWAIDIA RETICULATA: 



interior of dorsal valve. 



ElCHWALDIA RETICULATA: 



interior of ventral valve. 



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 appa- 

 rently folded back to form the false area D, and there does not usually 

 appear any evidence of a foramen at the apex. There is evidently a conti- 

 nuous 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 structure of the Briachiopoda, 

 that the pedicel should pass through the narrow slit between the diaphragm 

 and the outer shell, entirely outside of the proper rostral cavity ; still this 

 space has evidently served the animal for communication 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 



the diaphragm. 



