260 



Trans. Acad. Sci. of St. Louis. 



PAEAPHORHYNCHUS u. gen. 



Shell rostrate, or rather large size, coarsely plicate with 

 usually simple plications which extend nearly to the beak, 

 with a deep sinus in the pedicle valve and an elevated fold in 

 the brachial valve of the mature shell. Surface of both 

 valves marked by very fine longitudinal striae which increase 

 by bifurcation and intercalation. In the interior of the 



5 G 7 



Figures 1-7. A series of sections through the shell of Paraphorhynchus 

 elongatum, showing the structure of the hinge-plate with its cruralium-like 

 cavity, the medium septum and the crura of the brachial valve, and the 

 dental lamellae of the pedicle valve. 



pedicle valve there is a pair of vertical dental lamellae which 

 support the teeth and extend forward into the cavity of the 

 valve and between which there is a narrow muscular scar. In 

 the brachial valve a strong median septum supports poster- 

 iorly a hinge-plate with a median cruralium-like cavity, 

 anteriorly each lateral division of the hinge-plate is produced 



