PLATE Vlll-Continneci. 



Lept^na rhomboidahs, Wilckeiis. 



Fig:. 17- The exteriov of a larije pedicle-valve, which is unusually extended on the hinge-line and with ai;ute 

 cardinal extremities. 



Niagara grou] p. Luckport, N. T. 

 Fig. 18. An enlargement of the articTdating apparatus of the brachial valve ; showing the central groove 

 of the deltidial callosity, the lobes of the cardinal process, and the dental sockets with their 

 low, thick inner walls (crural plates). X 3. 

 Fig. 19. The interior of a brachial valve. 



Niagara group. Waldron, Indiana. 

 A view of the brachial valve; showing a foi-amen in the beak. 



A profile view of a sti-ongly geniculated s;ie<-imen ; showing the contour of the two valves. 

 An enlargement of the beaks of an old individual ; showing the great obliquity of the foramen in 

 the pedicle-valve, which penetrates the sulistanoe of the shell at a considerable distance in 

 advance of the apex ; and also the jierforation in the deltidinm of the ojiposite valve.- 

 A cardinal view of a sjiecimen where the deltidium of the pedicle-valve has been lost or absorbed 



and the space tilled by the callosity of the oiiposite valve which is jjerforated at the apex. 

 The interioi' of a brachial valve ; showing the aspect of the cardinal process from this point of 

 view, the character of the muscular scars, and the strong I'idge at the line of geniculation of 

 the valve. 

 The interior of a pedicle-valve ; showing the character of the muscular impressions. 

 An enlargement of the central cardinal portion of a brachial valve ; showing the deltidial callus, 

 and the slit formed by the receding or wearing of the apical pei'foi-ation. 

 Fig, 27. An enlargement of the intei-ior of the preceiiing specimen ; showing the same features, and also 

 the tubular opening into the I'ostral cavity between the divisions of the cardinal process. 

 Lower Helderberg grouj). Albany and SchoTiarie counties, N. Y. 

 The exterior of an exfoliated pedicle-valve ; showing very strong undulations and the groove left 



by the receding of the apical foramen. 

 The exterioi- of a pedicle-valve, in which the undulations are finer and much more luimej-ons than 

 usual. (The L. undulata of Vanuxem.) 



Corniferous limestone Western New York. 

 The exterior of a pedicle-valve. 

 The inteidor of a brachial valve. 



Waverly gi'oup. Mallets' Creek, Ohio. 



