CONTRIBUTIONS TO PALEONTOLOGY. 315 



X. NOTE ON THE GENUS EICHWALDIA. 



A KNOWLEDGE of the internal structure of the shell described as Atrypa 

 coralifera * in the second volume of the Palmontologjj of New York has 

 long been a desideratum. Specimens of this shell, with two or three 

 unsatisfactory casts from the Niagara shale of New York, remained for a 

 long time in my drawers, with a doubt expressed regarding their generic 

 relations, and were usually referred to by a name indicating the smooth 

 umbo of the ventral valve, which had apparently been denuded of the 

 reticulate covering. It was only after much delay, and by careful working 

 among the specimens of a similar species from Waldron, Indiana, that I 

 was able to ascertain the internal structure of the shell. 



While preparing to publish a note upon this fossil, imder the generic 

 name of Dictyonella, my attention was directed to the figures of Eich- 

 WALDiA in the Annual Report of the Canadian Geological Survey^ 1857-8. 

 The only feature in the figures, from which I inferred there might be 

 identity of generic character, was the naked or denuded beak of the 

 shell. I, therefore, deferred publication of my note upon the internal 

 structure, and subsequently obtained from Sir W. E. Logan the privilege 

 of examining the original specimens described by Mr. Billings. These 

 specimens were all silicified, and consisted of two separate valves with 

 one nearly entire specimen. Although to a person not suspecting other 

 than an ordinary smooth shell, these specimens might not indicate a 

 difierent external structure ; yet I conceive that the regularity in the 

 arrangement of the little points or nodes of silica (not the usual irregu- 

 larly distributed concentric nodes) indicates an original reticulate structure 

 which is obscured or destroyed by silicification. The E. suhtrigonalis of 

 Billings, therefore, I believe to have had originally a similar shell- 

 structure to those of the Niagara group, and to be congeneric with that 

 species. 



The following description of the genus, with observations thereon, is 

 copied from the Report cited above : 



* This species is very similar to, and by some authors has been considered identical with, Tere- 

 bratida capuvelli of England. 



