PLATE X. 
Plioflatecarpus hotjzeaui Dollo, IS89. 
Right quadrate, external side, natural size. Ciply (Hainault) near Mons. 
Upper Cretaceous (Upper Senonian); original in Brussels Museum. L. Dollo: 
Bull. Soc. belg. Geol., 1904, XVIII, pi. vi, fig. 6. 
Showing the tympanic operculum (o. t.) or thickened and calcified tympanic 
membrane, in adaptation to diving to great depths. 
