136 PALJEONTOLOGY OF NEW-YORK. 



Fig. 1 D. Front view of the last, showing the plications, which are 10 J 10. 



Fig. 1 B. Profile view of the same. 



Fig. 1 F. Cardinal view of another specimen, with the extremities extending beyond the greatest width 



of the shell below. 

 Fig. 1 o and h. Front view and profile of a specimen similar in form to 1 b, but having the plications 



10 J 10. The cardinal line is less than the width of the shell, and the extremities rounded. 

 Fig. 1 I, K. Front view and ventral valve of a cuboidal specimen, showing some irregularity in the 



development of the plications ; a single one in the sinus and two on the medial lobe being 



fully developed, with smaller ones on each side, while the lateral plications are six and seven. 



The following present some deviation from the prevailing forms, and approach to the 

 Var. B. iSip. dentatus of de Verneuil. The front of the medial lobe, in all of them, is 

 elevated higher than the centre of the same valve ; while in the previous ones, the greatest 

 elevation is in the centre of the shell, the front curving downwards. 



Fig. 1 L, M, N. Ventral, dorsal, and profile view of a small specimen, with the plications arranged thus : 

 5^5. 



Fig. 1 o, p, (1. Ventral, front, and profile view, having the same form and proportions as the last, but 

 having an additional plication upon each side. 



Fig. 1 R, 8, T, u. Ventral valve, front, cardinal, and profile views of the same specimen, which is re- 

 markably extended on the hinge line. This specimen has a single fully developed plication 

 in the sinus, and two on the mesial lobe, with the rudiment of another on each side of the 

 sinus and of the medial lobe, while the lateral plications are ten on each side. 



Position and locality. This species occurs in numerous and widely separated localities of 

 the Trenton limestone, being confined to the rocks of this period in the United States, and 

 unknown in New-York above the Utica slate, though this line of demarcation cannot be 

 recognized at the West. Within the State of New- York, it is found at Middleville, Trenton 

 Falls, Herkimer, Jacksonburgh, and other localities in the Mohawk valley. It is also found 

 at Turin, Watertown, and other places towards Lake Ontario, and is likewise known at 

 several places in the Champlain valley. It is found in great numbers at Maysville and 

 Frankfort ( Kentucky) , near Nashville ( Tennessee) , at Cincinnati and Oxford ( Ohio) , 

 at Madison ( Indiana) , at Mineral Point ( Wisconsin), and on the northwest shore of Lake 

 Michigan and towards Green Bay. It likewise occurs at several localities in Canada East 

 and West, showing a geographical distribution equal to the extent of the lower silurian 

 strata of our country. It appears likewise in the lower silurian strata of Russia and the 

 north of Europe, having there, as elsewhere, a wide geographical distribution. 



(State Collection.) 



