PLATE VIII— Continned. 

 LEPTiENA RHOMBOIDALIS, WilckenS. 



Fig. 17. The exterior of a large pedicle-valve, whicli is unusually extended on the hinge-line and with acute 

 cardinal extremities. 



Niag-ara g'roup. Lock-port, N. T. 

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

 of the deltidial callosity, the lohes 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 foj-amen in the beak. 



A profile view of a strong-ly geniculated specimen ; 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 substance of the shell at a considerable distance in 

 advance of the apex ; and also the perfoi-ation in the deltidium of the opposite valve. 

 A cardinal view of a specimen whei-e the deltidium of the jjedicle-valve has been lost or absorbed 



and tbe space filled by the callosity of the opposite valve which is perforated at the apex. 

 The interior of a brachial valve ; showing the aspect of the cardinal process fi'om this point of 

 view, the character of the musculai- scars, and the strong ridge 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 I'eceding or wearing of the apical pei'foration. 

 Fig. 27. An enlai'gement of the interior of the pi-eceding specimen ; showing the same features, and also 

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

 Lower Helderberg group. Albany and iSchoharie counties, N. T. 

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



by the receding of the apical foramen. 

 The exterior of a piedicle-valve, in which the undulation? are finer and much more numerous than 

 usual. (The L. nndulata of Vanoxem.) 



Coi'niferous limestone . Western New York. 

 The extei-ior of a pedicle-valve. 

 The interior of a brachial valve. 



Waverly group. Mallets' Creek, Ohio. 



Fig. 



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 31 



