io6 
Aug. F. Foerste 
Pachypora (Platyaxum) planostiolata, sp. nov. 
{Plate III, Fig. 55 .) 
At the bridge west of Pegram, specimens occur which differ 
from Platyaxum platys chiefly in their mode of growth. They 
form thin expansions, increasing in thickness by a succession of 
superimposed layers which often are more or less free toward the 
margin. The lower side of the corallum and of all of the free parts 
of the successive expansions is covered by a concentrically wrin- 
kled epitheca. The largest specimen at hand, when complete, 
must have had a diameter of about 25 cm., and a thickness at the 
center of at least 15 mm. The free parts of the expansions fre- 
quently are less than 2 mm. thick. 
The corallites are very oblique to the surface and have very 
depressed apertures. There is a great variation in the form of the 
aperture, depending in part on the state of preservation. In most 
well preserved specimens the lower edge or lip of the aperture is 
slightly convex and the anterior outline of this wall is distinctly, 
sometimes strongly convex, producing a lunate aperture. The 
upper margin of the aperture, formed by the general surface of the 
corallum, is often distinctly concave for a short distance anterior 
to the lower edge or lip. A semi-lunate mass or line of clay often 
appears in the aperture, indicating its form. In some specimens 
the lower edge or lip of the aperture is distinctly elevated along the 
median line, the elevation being bordered by narrow, though shal- 
low, depressions on either side. In these cases that part of the 
anterior margin of the lower lip which is anterior to the grooves 
often projects slightly farther forward^ while the median part is 
slightly indented, giving a slightly dentate appearance to the ante- 
rior outline of this lip. The median parts of the lower lip, when 
distinctly elevated, often are worn back, as in Platyaxum platys. 
In some worn specimens a distinct longitudinal ridge appears 
to be present on the interior of the corallite, along the upper wall; 
in others, it cannot be detected; possibly cross-sections might show 
it. About 7, sometimes 5, apertures occupy the width of 5 mm. 
This species does not appear to be a true Alveolites, although 
specimens congeneric with it appear to be referred usually to that 
genus. In Ccenites the corallites bend abruptly toward the surface 
meeting the latter almost at right angles, the walls being thickened 
abruptly near the surface. These features are not noticed in the 
