PLATE LXV. 



(Figures 1-3, fl;by G. B. SIMPSON ; 4, 6-9 by K. Emmons) 



Genus CONCHIDIUM, Linne. 



Page 231. 



CoNCHiDiuM DECUSSATUM, Whitcaves. 



Fig. 1. Ventral view of a specimen partially exfoliated in the iimlional region ; showing the fine, dupli- 

 cate j)lication and the delicate concentric lineation of the surface. 



Fig. 2. Doi'sal view of the umbonal portion of an internal cast ; .showing the cavity of the spondyliuni 

 and median sejitum of the pedicle-valve, and the genital markings about the beak. 



Niagara group. Grand Rap'iriit of the Saskatchetoaii River, British Aiiwrica. 



CONCHIDIUM LAQUEATUM, Coiliad (=PeNTAMERUS NOBILIS, KmillOlls). 



Fig. 3. An anterior \iew of a poi'tion of the interior, looking into the chamber produced by the union of 

 the spondylium and septal plates j showing the curvature of the latter, their explanate upi)ei- 

 surfaces, and the foreshortened crural apophyses. 



Fig. .1. Another view of the same specimen ; showing the spondylium with a portion of the median sep- 

 tvmi adhering, and the extent of the septal plates and crural processes. 



Figs. 4, H, 9. Dorsal, ventral and profile views of an internal cast of a rather narrow shell ; showing the 

 contour, character of the plication and smooth umbonal slopes. 



Fig. 7. Longitudinal section of conjoined valves ; showing the extent of the median septum of the pedicle- 

 valve (juite to the anterior margin of the valve, its concave anterior eilge, the projecting ex- 

 tremity of the spondylium, and in the brachial valve, the relatively .short spondylium and 

 septa, and the projection of the crural apophyses. 



Fig. 8. An internal cast of a brachial valve which retaines the jirevailing broader form of the species. 

 Niagara <lolomites. Delphi, Indiana. 



