GENUS EICHWALDIA. 277 



E. RETICULATA. 



Longitudinal section of the two valves. 



In the longitudinal section of the shell, fig. 7, it will be noticed that 

 the apex of the dorsal valve, or cardinal process, extends far into the 

 cavity of the ventral valve, while the cardinal muscle was apparently 

 attached just below the margin of the diaphragm or transverse septum of 

 the opposite valve. The great extent and ventral extension of the longitu- 

 dinal septum of the dorsal valve is a remarkable feature. 



The mode of articulation of the valves is much in accordance with the 

 recent Rhyncbonellidse, except that the dental lamellae are not distinctly 

 developed. At the present time, however, I am far from feeling satisfied 

 regarding the true relations of this peculiar genus. 



The figures given illustrate all that we know at present in regard to the 

 interior structure of this genus, which is represented by several very pretty 

 species. I hope that the author of the generic name may feel disposed to 

 accept this contribution of facts regarding its more important characters, as 

 aiding in the establishment of one of the most interesting genera among 

 the Brachiopoda. 



Genus Eichwaldia (Billings), 1858. 

 Generic characters — as emended. 



Shells ovate or subtrigonal ; with or without mesial fold and sinus. 

 Ventral valve obscurely perforate on the umbo; apex acute and entire, 

 the space beneath it occupied by an imperforate concave plate ; the inte- 

 rior of the rostral cavity lined by a transverse septum or diaphragm, below 

 which is the pedicel [?] opening. Dorsal valve with a slender cardinal process, 

 and a very elevated medio-longitudinal septum. Valves articulating by a 

 long" narrow groove in the cardino-lateral margins of the dorsal valve, in 

 which rest the elevated corresponding margins of the opposite valve. 



Surface of the shell reticulate ; the texture solid and fibrous beneath. 



The American species known at present are : 



jE. subtrigonalis, Billings : Lower Silurian, Canada. 



E. coralifera, Hall : Niagara, New-York. 



E. reticulata, Hall : Niagara, Indiana. 



E. gibbosa, Hall : Niagara, Tennessee. 



E. coucinna, Hall : Niagara or Lower Helderberg, Tennessee. 



Eichwaldia subtrigonalis (Billings). 

 Report on the Geological Survey of Canada, 1858, page 192. 



