. THE BRITISH FERNS. 
Genus XIX: OPHIOGLOSSUM, Linneus. 
Gen. CHar.—Fructification in a distichous spike, terminating a 
distinct branch of the frond, or on a distinct frond. Spore-cases 
uniserial along each margin of the compressed spike, with which 
they are connate, horizontal, globose, bursting in two equal hemi- 
spherical valves. Veins uniformly reticulated in roundish or 
elongated hexagonal areoles, sometimes from an indistinct costa, 
occasionally obscure; veinlets free, included in the ultimate areoles, 
sometimes wanting. 
Fronds subcarnose, two- or many-branched ; the sterile branch 
simple dichotomously parted or palmate-lobate, the fertile simple; 
the fronds sometimes simple, the sterile and fertile ones being distinct 
and dissimilar. 
Caudex corm-like, fleshy, subglobose, or short cylindrical ovate. 
The genus Ophioglossum is the type of the order Ophioglossacem 
already mentioned. under the preceding genus as differing from the 
generality of Ferns, in having ringless spore-cases and straight ver- 
nation. The genus is itself allied to Botrychium in general habit, 
but differs in having the branches of its two kinds of fronds in the 
British species quite simple or undivided, instead of being pinnate 
and bipinnate respectively as they are in that genus. The principal 
distinction between the two genera, however, resides in the nature of 
the fertile branches, which form simple distichous spikes in Ophio- 
glossum, and more or less branched panicles in Botrychium. 
Though in many respects similar in their habit, there is one 
remarkable difference between Ophioglossum and Botrychium in 
respect to the manner of their development. In Botrychium, as we 
have already seen, the succeeding years’ fronds are found within 
the base of the growing stems, but in Ophioglossum a lateral bud 
is developed by the side of the eurrent year's fronds. 
In the present family there is some variety of character among 

