R. P. Whitfield—Lingula in the Trenton Limestones. 473 
Elderi, after the discoverer, and a full description will be given, 
with figures, in the forthcoming Paleontological Report of the 
Geological Survey of Wisconsin. 
e casts represent a species of moderate size, the average 
being about seven-eighths of an inch in length; the general 
outline is somewhat quadrate, the lateral margins being sub- 
othe and a little convex, the upper end very obtusely angu- 
ar or pointed, and the base rounded; the valves are convex, 
but the dorsal the most strongly so. The shell, when preserved, 
is smooth with very fine concentric lines, but presenting a pol- 
ished appearance. The peculiar features are found in the pres- 
ervation of the imprints left by the muscular and vascular 
scars on the shell, as copied on these internal casts, thus afford- 
ing means of comparison with the corresponding organs of the 
living forms of the genus. These markings correspond more 
nearly to those of Z. anatina Lam. than do those of any other 
been able to trace all the elements of the muscular system, nor 
to detect the divisions between those forming the larger scars; 
Some of which, in the recent forms, are seen to be composed of 
three or four elements; but where they are impressed so lightly 
on the shell and yet leave the trace of their advance over its 
