70 METZGERIACEAE 
fornia. This adaptation for carrying the plant over a season of 
drought will doubtless be found, when the species from the more 
arid regions of the earth come to be better known, to be more 
common among the Hepaticae and Anthocerotes than has been 
generally supposed, as has already been remarked by Herr 
Stephani. From the above showing it. will be seen that the occur- 
rence of tubers in Geothallus can receive no emphasis in the gen- 
eric diagnosis, inasmuch as this is elsewhere evidently а specific 
rather than a generic character. 
„13. RICCARDIA S. Е. Gray, [as Riccardius] Nat. Arr. Brit. РІ. 
08% 1821. 
Aneura Dumort. Comm. Bot. 115. 1822. 
Gametophore a pinnately, palmately, or subdichotomously 
branched, rarely almost simple, somewhat fleshy thallus, composed, 
for the most part, of several layers of cells, with the interior cells 
considerably larger and more elongated than those of the surface, 
usually undifferentiated into costa and lamina though sometimes 
provided with a unistratose border, this, in its best development, 
giving the thallus, especially the younger branches, the appearance 
of being broadly costate. ^ Root-hairs few. Monoicous, dioicous, 
or rarely paroicous, occasionally, perhaps, polyoicous.  Antheridia 
spherical, immersed singly in loculi, commonly arranged in two 
parallel rows on a small, rounded, or most often, oblong or linear, 
lateral branch. Archegonia several, on a short subovate lateral 
branch, this by subsequent growth of the main thallus sometimes 
appearing to be attached ventrally ; margin of the 9 branch usu- 
ally furnished with numerous narrow laciniae, these often produced 
calyptra represented only by the fringed margin of the Ф branch, 
this becoming more or less coalesced with the base of the calyptra 
and usually quite inconspicuous, 
porogonium an oval or oblong-ellipsoidal capsule on asome- 
what long seta. Capsule before dehiscence with a short internal axile 
column at the apex, formed as if by continuation of the inner of 
the two layers of cells composing the capsule-wall, this column 
separating, on dehiscence, into four parts—the “ elater-bearers "— 
