298 
The American Geologist. 
May. 1904. 
the transver.se axis and becoming- quite pronounced and turn- 
ing abruptly upward in front. Anterior and lateral edges of 
the valve notched or serrate. 
Brachial valve: M'oderatel}- convex, with a tendency to 
somewhat greater convexity in gerontic specimens. Mesial fold 
beginning about the middle of the valve and becoming very dis- 
tinct in front. Margin of valve serrate as in the corresponding 
member. 
Character of surface markings: Surface of each valve cov-. 
ered with from twelve to twenty-eight low, rounded plications 
which are well developed around the anterio-lateral edges but 
obsolete or wanting over the umbonal regions. From four to 
eight plications occupy the sinus and an equal number on the 
fold, while from six to ten cover each lateral portion of the 
valves. The space between the plications narrow and angular. 
Exf^huiatioit of Figures. 
Rhynchopora illinoiscnsis (Worthen). 
Fig. I, brachial view, fig. 2, pedicle view, fig. 3, anterior view. 
