374 Proceedings of the Oliio State Academy of Science. 



valve and by the withdrawal of the brachial valve far within the 

 pedicle valve, as shown in Fig. 9 c and e. 



This contact causes a plane of weakness along which the 





e f g 



Fig. 9. — Prodiictus cestriensis. 



a. — A view of a pedicle valve, a portion of the margin of which 



has been broken away. 



b. — An internal view of a brachial valve, showing the abrupt, for- 



ward bend of this valve. 



c. — A dorsal view, showing the concave structure of the brachial 



valve. 



d. — A view of a pedicle valve showing the beak and concentric 



wrinkles. 



e. — A dorsal view showing especially the concavit}' of the brachial 



valve. 

 f and g. — Portions of the same specimen, which have separated 

 along the plane of weakness caused by the abrupt forward 

 bend of the anterior half from the flat posterior half of 

 the brachial valve. 



shells of many specimens break (Fig. 9 f and g). Its smaller 

 size and coarser plications readily separate it from P. pilei- 

 formis, the other JNIaxville species. 



