PLATE X. 



(Figures 1-14, 16, IS-JS by K. 1'. Whitkield; 16, 17 by F li. Mkkk.) 



Leg^ncl. U. Deltldium. j. Cariliiiiil process. 



A. Cardinal area. c. (Jrurii. 



I. Umbo-lateral slope.i. s. Meiiiati neptura. 



t Teeth, a. A<kluctor scafs. 



d. Dental lamellae. r. Didiictoi- scars, 



b. Dental sockets. 



Genus ORTIIOTIIETES, Fischku i.k W Ai,r)iiKiM. 



Orthothetes Chemungensis, Coiuad, viir. Pandoka, Billings. 



Fig. 1. A view from the bi'achial valve ; showing the cardinal area and deltidiura of tUe oppi'site valve. 



Corniferous limestone. Caledonia, N. Y. 

 Fig-. 2. The intei-ior of a brachial valve, drawn from a gutta-percha impre.ssion ; showing the muscular 

 area, and, imperfectly, the cardinal process. 



Schoharie grit. Schoharie, N. Y. 



Fig. 3. The interior of a larger brachial valve ; showing with more accuracy the crural plates and the 

 adductor scars. 

 Plate IX, Fig. 30. — An enlargement of a part of the hinge area, the cardinal process, crural 

 plates and muscular impi'essions of the preceding specimen. 



Fig. 4. The interior of a pedicle-valve; showing the low deltidiuni, with unsui>ported teeth, the adductor 

 and iliductor scars. 



Corniferous limestone. Caledonia, N. Y. 

 Fig. 5. The interior of a pedicle-valve, drawn from a gutta-percha impi'ession. 



Schoharie grit. Schoharie, N. Y. 

 Fig. 6. An internal cast of the pedicle-valve ; .showing the Habellate diductors and the impression of a 

 broad median ridge. 



Corniferous limestone. Western New York. 



Orthothetes ChEiMungensis, Connul, vjir. ai.ternata, Hall. 



Fig. 7. The interior vt the brachial valve ; showing the characteristic cardinal process. 

 Hamilton group. Caiiandaigua Lake, N. Y. 



Orthothetes Chemungensis, Conrad, var. arctostriata, PLill. 



Fig. 8. An internal cast of the pedicle-valve ; .showing the imju'ession left by the rather unusual develop- 

 ment of the ridges surrounding the adductor scars and miiting in the median line sepaiatiug 

 the diviuctors. This ridge is not a septum but merely the thickening of the edges of the mus- 

 culai- scars. X '^. 



Hamilton group. Western New York. 



Orthothetes Chemungensis, Connul. 



Fig. 9. A caidinal view of a specimen ; showing the irregular form of the shell, the usual width of the 

 area, and the character of the deltiilium. 



Chemung group. South-western New York. 

 For further illustration, see Palaeontology of New York, Volume IV, [ilates ix and x. 



Genus DERBYA. Waagen. 



Page 261 



Derbya crassa, Meek ;ind Hayilen. 



Fig. 10. The interior of a brachial valve ; showing the cardinal process and muscular impi-essions. The 

 former is repi'esented as having the lobes upon its edge and too acutely angular. 



Fig. 11. The interior of a pedicle-valve, with strong median septum dividing the muscular area, and 

 highly developed teeth projecting into the cavity of the valve. 

 Coal Measures. Near Winter.iet, Iowa. 



