374 rroccc(liii(/s of the Ohio State .Icadcuiy of Science. 



valve and by the withdrawal (>f the brachial valve far within the 

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



This contact causes a plane of weakness along which the 



/•'^.^ 



I 



e f g 



Pig. 9. — Prodiictus ccstriensis. 



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

 has been broken away. 



b. — An interna] view of a brachial vahe, showing the alirupt, for- 



ward bend of this valve. 



c. — A dorsal view, showing the concave structure of the l)rachial 



valve. 



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



wrinkles. 

 e. — -A dorsal view showing especially the concavity 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. pilci- 

 formis, the other Maxville species. 



