310 PALEONTOLOGY OF NEW YORK. 



this smooth spot is present and it is always accompanied by a decided incurva- 

 ture of the apex of the valve. 



The condition of the edges of this aperture has convinced some observers of 

 the probable atrophy of the pedicle, and the fixation of the shell by solid 

 cementation at this point. It must, however, be borne in mind that among the 





Fig. 241. Fig. Hi. 



Eichwaldia suhtrigonalis, Billing-s. 



Dorsal and ventral views of a silicified young shell retaining the pedicle; showing its protrusion from the unibona 



aperture. From photographs of the original specimen described by Btllings. 



original illustrations of the type-species, E. suhtrigonalis, Mr. Billings represented 

 a young shell in a silicified condition, with an extended pedicle protruding 

 from, or at least covering the aperture represented by the bare spot. Through 

 favor of Mr. J. F. Whiteaves, of the Geological Survey of Canada, we have 

 been furnished with photographs and drawings of this specimen, and notwith- 

 standing this remarkable instance of the replacement of a soft organ by silica, 

 there seems, from this evidence, to be no reason to doubt that the umbonal 

 aperture was solely for the passage of the pedicle. Such being the case, it will 

 naturally follow that the internal plate or umbonal diaphragm is a modified 

 condition of the deltidium or of the deltidial plates, probably the former. 



The earliest species of this genus, of which we have information, is the type- 

 form, E. suhtrigonalis, Billings, which was described from the Black River lime- 

 stone at Paquette's Rapids, on the Ottawa River. The other American species 

 are all from the Niagara faunas, E. coralifera, Hall, occurring in the New York 

 shales, E. reticulata, Hall, in the calcareous shales at Waldron, Indiana, E. gib- 

 hosa and E. concinna. Hall, in the limestones of western Tennessee, and 

 E. Anticostiensis, Billings, from Anticosti. Eichwaldia Capewelli, Davidson, 

 appears to be not uncommon in the Wenlock shales of England, and has been 

 identified by Lindstrom, in the Island of Gotland. Barrande has illustrated 

 three species from the stages E and G, namely, E. Dormitzeri, E. Branikensis, 

 E. Bohemica, Barrande. 



