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broken into shreds. In most specimens no trace of these films 
is found, there is no thickening of the valves anteriorly, and the 
exterior surface is comparatively smooth except where interrupted 
by the stronger radiating striae. Possibly the films are produced 
in rapid succession by the mantle, each later film more or less 
crowding out of its road the earlier films, until the thicker, solid 
shell material of valves is produced. As a matter of fact, the 
films should be investigated by means of a series of thin sections, 
under the microscope, in order to determine their more intimate 
structure, before theorizing as to their origin. Shells with this 
structure have a considerable vertical range. They are most 
abundant in the Eden, ranging from the lowest strata immediately 
above the Fulton layer into the Southgate layer which furnished 
the types. Similar specimens occur also in the Waynesville 
and Liberty members of the Richmond, although the thickening 
at these upper horizons usually is less prominent. Some of the 
poorly preserved, silicified specimens from the Curdsville bed 
appear to have had a similar structure. Possibly this structure 
is of a more extended range, and may occur sporadically in almost 
any species of the genus. At any rate, it is not a constant char- 
acteristic of any species, as originally supposed by James. At 
least, in many specimens no trace of it remains. 
The oblique wrinkles along the hinge-line, described and rather 
inadequately figured by Meek, occur not only in the lower and 
middle Eden but also in the Waynesville beds. They are not 
constant at any horizon, and do not characterize any species. 
They are likely to occur in any of the larger specimens, though 
specimens of medium size also occasionally show the oblique 
wrinkles. 
Under Leptaena aspera, James stated that the cardinal line of 
the brachial valve is straight, and has a crenulated appearance, 
most conspicuous when held to a strong light. This crenulated 
appearance is not due to any unevenness of surface, either of the 
hinge-area or of the exterior surface of the valves. It is seen only 
when light is transmitted through the shell substance, and is most 
distinct in the more translucent shells. The number of wrinkles 
varies from 6 to II in a width of 3 mm. As viewed ordinarily, the 
wrinkles appear at right angles with the hinge-line and therefore 
have no connection with the oblique wrinkles seen on the exterior of 
the valves. They occur also when viewing the brachial valve by 
