PLATE LXV. 



(Kifrures 1-3, S^by G. B. Simpson ; 4, 6-9 by K. Kmhonb.) 



Genus CONCHIDIUM, Linn^. 



I'age 'J31. 



CoNCHiDiUM DECUSSATUM, Whitcaves. 



¥ig. 1. Ventral view of a sjiecinien partially exfoliated in the umbonal region ; showing the fine, dupli- 

 cate plication and the delicate concentric lineation of the surface. 



Vig. "i. Dorsal view of the umbonal jiortion of an internal cast ; showing the cavity of the spondylium 

 and median se])tum of the pedicle-valve, and the genital markings atjout Ihe beak. 



Niagara group. O^rand Rapids of the Saskatcheioan River, Britwh Ainenca. 



C0NCHIDIU.M LAQUEATUM, Coiiiiid (=Pentameru8 NOBiLis, Eminoiis). 



Fig. 3. An anterior view of a jwrtion of the interior, looking into the chamber produced by the union of 

 the sjiondyliuin and septal plates ; showing the curvature of the latter, their explanate upper 

 surfaces, and the foreshortened crural apophyses. 



Pig. .■>. Another \new of the same specimen ; showing the spondylium with a portion of the median sep- 

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



FigB. 4, 6, 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. 



Pig. 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 anteiior edge, 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. 



Kg. 8. An internal cast of a brachial valve which i-etaines the prevailing broader form of the species. 

 Niagara dolomites. Delphi, Indiana. 



