136 PALEONTOLOGY OF NEW-YORK. 
Fig. 1 p. Front view of the last, showing the plications, which are 10 4 10. 
Fig. 1 £. Profile view of the same. 
Fig 
. | x, Cardinal view of another specimen, with the extremities extending beyond the greatest width 
of the shell below. 
Fig. 1g and u. Front view and profile of a specimen similar in form to 1 B, but having the plications 
10 2 10. ‘The cardinal line is less than the width of the shell, and the extremities rounded. 
Fig. 1 1, x. 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. Sp. dentatus of pr Vernevuit. 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 1, m, N. Ventral, dorsal, and profile view of a small specimen, with the plications arranged thus: 
5 4 5. j 
3 
Fig. 1 0, p, a. 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,s, T, v. Ventral valve, front, cardinal, and profile views of the same specimen, mich is Te- 
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 Jower silurian strata of Russia and the 
north of Europe, having there, as elsewhere, a wide geographical distribution, 
(State Collection.) 
