Cumings — Morphogenesis of Platystrojphia. 



15 



oiforata from Wesenberg,* Russia, shows five plications in the 

 sinus. To the left is shown the arrangement of these plica- 

 tions. At the apex there is a single plication which immedi- 

 ately bifurcates. Then a plication is implanted between the 

 two thus formed, and immediately bifurcates giving four pli- 

 cations. Between the two last formed is now implanted 



6 



Fig. 6. Platystrophia biforata (P. lynx of authors) from Pulkowa, Russia. 

 A-D ventral, anterior, dorsal, and posterior views ; E, stage II. (see C) drawn 

 separately ; F, stage i". (see E) drawn separately ; G, profile, showing strong 

 incurvature and great size of dorsal valve. f Collection U. S. National Museum. 



another plication, making five. Fig. 21V, of the dorsal valve 

 of the same specimen, shows six plications on the fold, which as 

 seen in the diagram to the left originate as follows : first, two 



*This specimen and the next to be described were labeled by F. Roemer. 

 f All figures natural size unless otherwise stated. 



