EXPLANATION OF THE ILLUSTRATION 
Crossorueca saairrara ( Lesquereux) Sellards 
A specimen of a pinna, showing the typical sagit- 
tate form of the ‘“sporophyll.’’ Carboniferous : 
Allegheny Formation. Mazon Creek, Illinois. 
Three fourths natural size. Harvard Botanical Mu- 
seum (Paleobotany) No. 19703 (F.O. Thompson 
Collection). 
