No. 634] BIONOMICS OF MELLITA 



437 



cular even in specimens of maximal size, and the ventral surface 

 of the disk practically flat (Fig. 2).- It frequently happens, 

 however, that the central region of the body becomes relatively 

 thicker than in the flat, circular sea-plates, and in these indi- 

 viduals there are several noteworthy departures from the typical 

 structure. Anteriorly the disk is more wedge-shaped in vertical 



section ; the anterior antimere projects forward, forming a sharp 

 "nose," or entering point, which presumably facilitates bur- 

 rowing (Fig. 3 A ). The antero-lateral radius on either side 



