Notes ON AMERICAN FERNS—XII 115 
continuous, linear indusium, common to the very numer- 
ous contiguous sori associated in a narrow, intramar- 
ginal line, would seem to offer sharp distinctions to 
the soriation of C. californica, in which the sori are 
almost invariably solitary, having each a separate, 
short, roundish-lunate indusium attached at the trans- 
versely enlarged vein-tip to a slender, almost saccate 
marginal tooth on either side; but it will be found that 
the modification of leaf margin is similar in both species, 
and that the greater prominence of the marginal teeth 
in C. californica and the development of solitary sori 
in this species are characters directly correlated with 
the greater dissection of the lamina. The fronds of 
Pellaea densa are nearly always completely fertile, with 
long, subentire, linear segments; but in the rare semi- 
fertile fronds (these having serrate segments) or even 
in oceasional wholly fertile specimens with unusually 
short segments the sori may be interruptedly continuous, 
with the indusia lobed, correspondingly, or even dis- 
continuous. Some such specimens have actually been 
determined as C. californica. In habit, rhizome scales, 
absence of paleaceous or hairy covering of lamina, 
and development of a true membranous indusium the 
two species are strikingly alike and are undoubtedly 
congeneric. Their proper generic reference is not so 
clear, however. In. the characters just enumerated 
they are at variance with a majority of the species of 
Cheilanthes, as that genus is now regarded, yet there 
are several species variously referred to either Cheilan- 
thes or Pellaea to which they are closely akin, the whole 
assemblage perhaps constituting a separate genus. 
Thus, Cheilanthes californica, the type of Nuttall’s 
unpublished genus Aspidotis, is closely similar to the 
African C. Schimperi Kunze, and Pellaea densa is no 
less closely related to the Himalayan Cheilanthes nitidula 
Hook. and the Mexican and Central American C. intra- 
