PLATE UXVI-CoDtiDued. 



visceral canal, the outer opening being visible at the apex of the plate. This canal is, how- 

 ever, closed by testaceous deposit, and the median division of the plate on its upper surface 

 largely obscured from the same cause. 

 Fig. 90. The interior of the umbonal portion of the pedicle-valve ; showing the dental plates and muscular 

 impressions. 



Oriskany sandstone. Onmberland, MaryJand. 



Genus AMPHIGENIA, Hall. 



Page 252. 



Ahfhioenia elongata, Hall. 



See Plates 73, 74. 

 Fig. 9. The cardinal portion of the brachial valve ; showing the form of the hinge-plate, its median 

 depression, the opening of the visceral foramen, a portion of the septal plates and the branch- 

 ing vascular sinuses. 



Comiferous limestone. Le Boy, New York. 



Genus RENSSEL^RIA, Hall. 



Page 254. 



Renssel^ria ovoides, Eaton. 



See Plate 75. 

 Fig. 16. The hinge-plate enlarged ; showing its form, the opening of the visceral canal, the highly 



developed crural plates ; also the elongate dental sockets and outer socket walls. X 2. 

 Fig. 18. A cast of the hinge-plate ; showing the unbroken filling of the visceral canal. 

 Oriskany sandstone. The Helderbergs, New York. 



Renssel^ria mutabilis, Hall. 

 See tigTires l-3a. 

 Pigc. 21, 23. Dorsal and profile views of a broad, ovate form with elevated umbo, open delthyrium, well- 

 defined cardinal slopes and rather coarse surface plication. 



Ix>wer Helderberg group. Becraft's Monmtain, Columbia county. New York. 



Rensseljeria ^quiradlata, Conrad. _ 



Figs. 23, 24, 2.5. Dorsal, profile and front views of one of the original specimens ; showing the form of the 

 shell and the character of its plication. 



Lower Helderberg group (Upper Pentamerus limestone). Schoharie, New York. 



Rens8ela;ria elliptica, Hall. 



Figs. 36, 27, 28. Dorsal, profile and front views of the original specimen ; showing the foi-m and convexity 

 of the shell. 



Lower Helderberg group (Shaly limestone). Schoharie, New York. 



