e Es attached by a point, or more or less by the base or sides, 
_ and are of various forms, being reniform, subrotund, oval, 
= or oblong, sometimes very small (squamiform). Thei 
the form of a cup (calyciform), the margin being more or le 
^ : — (semicalyciform). 
ON GENERA AND SPECIES. 
INDUSIUM. 
The sori are either naked or furnished with a specia 
covering called the indusium, or involucrum by some, which — 
presents many well marked different forms, and is highly ` 
important for distinguishing genera; it consists of thre 
kinds— special, accessory, and universal. True or special ` 
indusia are more or less membranous, or thick and firm 
in texture, and rise from the receptacles to which they are 
attached in different ways. Some rise in the form of ai 
orbicular dise, covering the sorus in the form of a shield 
(peltate); more frequently they are attached on the interio 
or exterior side of the receptacle ; such are termed lateral, 
which open like a lid (operculiform) when attached on the 
side next the costa, interior, and when on the side next o 
on the margin exterior. 
Lateral indusia partake of the form of the sori, being 
round, oblong, or linear; in punctiform sori they are 
surface is flat, vaulted, or when attached by their sides - 
cucculate, their free margin being entire or variousl 
lacinated or fringed, ` ` | 
Besides these two modes of attachment there is a third 
kind, in which the indusium is attached all round the recep- _ 
tacle—it is at first globose, and includes the sporan 
but ultimately their apex opens and widens, thus assumi 
entire or deeply laciniated, even to be like a fringe; some- 
times the attachment is only half round the rece} pa 
