274 TWENTIETH EEPORT ON THE STATE CABINET. 



XI. NOTE ON THE GENUS EICHWALDIA. 



A knowledge of the internal structure of the shell described as Atryya 

 coralifera* in the second volume of the PalaBontology 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, under the generic name 

 of DiCTYONELLA, my attention was directed to the figures of Eichwaldia 

 in the Annual Report of the Canadian Geol. Survey (1857-8). The only fea- 

 ture 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 different external structure ; yet I 

 conceive that the regularity in the arrangement of the little points or nodes 

 of silica (not the usual irregularly distributed concentric nodes) indicates 

 an original reticulate structure, which is obscured or destroyed by silicifi- 

 cation. The E. suhtrigonalh 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 : 



'' Genus Eichwaldia (Billings). 



'' Generic Characters. — Large valve perforated on the umbo for the passage of the 

 peduncle; the place of the foramen beneath the beak occupied by an imperforate 

 concave plate, the interior divided by an obscure medio-lougitudinal ridge; interior 

 of smaller valve divided throughout from the beak to the front by a very prominent 

 medio-longitudinal ridge; no hinge, teeth, sockets, or other articulating apparatus 

 in either valve. 



'•'After a great deal of examination and comparison, I have not been able to refer 

 the species for which the above generic name is proposed to any of the described 

 genera. Although several silicified specimens exhibiting the interior have been ob- 

 tained, they do not show any muscular impressions. The perforation on the back 

 of the beak was at first supposed to be a fracture, but we have now specimens which 



* This .«peeies is very similar to, and by some authors has been considered identical 

 with, Terebratula capewelli of England. 



