THE MARSH FERN TRIBE. 127 



means a little shield, in allusion to the shape of the in- 

 dusium. Many of the common names given to members 

 of the genus are also derived from this shape. Dryopteris, 

 sometimes used instead of Aspidium, is also from the 

 Greek and literally means oak-fern. There are upwards 

 of one hundred and fifty species distributed throughout 

 the world. It is probable that the generic name 

 Nephrodium will ultimately be used for these species in 

 America. It is the name commonly used abroad. 



