PLATE X. 



(Hgures 1-U, 16, 18-iS by K. 1*. VVuitfielu; 16, 17 by F. li. Mkkk.) 



Legend. D. Deltidium. j. Cai-clinal proceaa. 



A. Cardinal area. c. (^Irura. 



I. Unibo-lateral slopes. s. Median septum. 



t Teeth. a. Adductor scare, 



d. Dental lamellae. r. Didnctor scars. 



1). Dental sockets. 



Genus ORTIIOTHETES, Fischkr dk Wai.diieim. 



ORTHOTHETE8 Chemungensis, Coiinitl, viir. Pandora, Billings. 



Fig. 1. A view from the bi'achial valve ; showing the cardinal area and deltidiimi of the oppcsite valve. 



Corniferous limestone. Caledonia, N. Y. 

 Fig. 2. The interior of a brachial valve, drawn from a gutta-percha impression ; showing the muscular 

 area, and, imperfectly, the cai'dinal process. 

 Schohai-ie grit. Schoharie, N. T. 

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

 adductor scars. 

 Platb IX, Fig. 30. — An enlai'gement of a part of the hinge area, the cardinal process, crural 

 plates and muscular impressions of the pi'eceding specimen. 

 Pig. 4. The interior of a pedicle-valve j showing the low deltidium, with unsupported teeth, the adductor 

 and diductor scars. 



Corniferous limestone. Caledonia, N. T. 

 Fig. f). The interior of a pedicle-valve, drawn from a gutta-pei-cha impi'ession. 



Schoharie grit. Schotiarle, N. Y. 

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

 broad median ridge. 



Coi-niferous limestone. Westerti New Ywk. 



Orthothetes Chemungensis, Conrad, var. alternata, Hull. 



Fig. 7. The interior of the brachial valve ; showing the characteristic cardinal pro<tes.s. 

 Hamilton group. Canandaigua Lake, N. Y. 



Orthothetes Chemungensis, Conrad, var. arctostriata, Hall. 



Fig. S. An internal cast of the pedicle-valve ; showing the impression left by the rather unusual develop- 

 ment of the ridges surrounding the adductor scars and uniting in the median line separating 

 the (iiductors. This i-idge is not a septum but merely the thickening of the edges of the mus- 

 cular scars. X 2. 



Hamilton group. Western New Ywk. 



Orthothetes Chemungensis, Conrad. 



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

 area, and the character of the deltidium. 



Chemung group. South-western New York. 

 For further illustration, see PaliEontology of New York, Volume IV, plates ix and x. 



Genus DERBYA. Waagen. 



Page 261. 



Derbya crassa, Meek and Hayden. 



Fig. lU. The interior of a brachial valve ; showing the cardinal process and muscular impressions. The 

 former is represented as having the lobes upon its edge and too acutely angular. 



Fig. 11. The inteiior 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. 



