PLATE VIII—Continued. 
Lept^na rhomboidalis, Wilckens. 
Fig’. 17. The exterior of a large pedicle-valve, which is unusually extended on the hinge-line and with acute 
cardinal extremities. 
Niagara group. Lockport, N. T. 
Fig. 18. An enlargement of the articulating 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. 
Fig. 20. A view of the brachial valve; showing a foramen in the beak. 
Fig. 21. A profile view of a strongly geniculated specimen ; showing the contour of the two valves. 
Fig. 22. 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 perforation in the deltidium of the opposite valve. 
Fig. 23. A cardinal view of a specimen where the deltidium of the pedicle-valve has been lost or absorbed 
and the space filled by the callosity of the opposite valve which is perforated at the apex. 
Fig. 24. The interior 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 ridge at the line of geniculation of 
the valve. 
Fig. 25.’ The interior of a pedicle-valve; showing the character of the muscular impressions. 
Fig. 26. 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 perforation. 
Fig. 27. An enlargement of the interior of the preceding specimen ; showing the same features, and also 
the tubular opening into the rostral cavity between the divisions of the cardinal process. 
Lower Helderberg group. Albany and Schoharie counties, N. F. 
Fig. 28. The exterior of an exfoliated pedicle-valve ; showing very strong undulations and the groove left 
by the receding of the apical foramen. 
Fig. 29. The exterior of a pedicle-valve, in which the undulations are finer and much more numerous than 
usual. (The L. undulata of Vandxem.) 
Corniferous limestone. Western New York. 
Fig. 30. The exterior of a pedicle-valve. 
Fig. 31. The interior of a brachial valve. 
Waverly group. Mallets' Creek, Ohio. 
