LlOEHYNCHUS ROBXJSTUS, Hall. 



Page 365. 



Figs. 18, 19. Ventral and cardinal views of a sharply marked internal cast of 

 large size; showing the muscular impressions of both valves and the vascu- 

 lar sinuses in the pedicle-valve radiating from the impression left by the 

 umbonal testaceous callosity. 

 Chemung group. Steuben county, N. Y. 



CONCHIDIUM EXP0NEN8, Hall. 



Page 366. 



Figs. 20-23. Interiors of pedicle (figs. 20, 21) and brachial valves (figs. 22, 23). 

 Niagara group (Halysites bed). Louisville, Kentucky. 



CoNCHiDiuM Nettelrothi, Hall. 



Page 366. 



Figs. 24, 25. Dorsal and lateral views . (After Nettelroth.) 

 Corniferous limestone. Near Louisville, Kentucky. 



This fossil published by Mr. Nettelroth, under the name of Pentamerus 

 Knightii (Fossil Shells of Kentucky), is referred by him to the Corniferous 

 limestone. The form and entire external characters of the species are so sim- 

 ilar to those from the Niagara formation in the vicinity of the Falls of Ohio 

 and elsewhere, that the reference to this geologic horizon is probably errone- 

 ous. The form is .very similar to Conchidium hiloculare, Linne, from the 

 Island of Gotland; and to some varieties of Conchidium nysius, Niagara 

 group, near Louisville, Ky., that one can scarcely doubt its Silurian age. 



395 



