RHACOMITRIUM. 149 



the point of view of greater convenience. All the species except 

 J?, canescens and R. lanuginosum, are, as in Grimmia, confined to 

 rocks. The peculiar areolation of the leaf, especially at the base, 

 is at once recognised under the microscope, and identifies the 

 genus at a glance. Many of the species from their long prostrate 

 stems, numerous short branches, and apparently lateral fructifica- 

 tion, bear a great outward resemblance to the Hypnoid Mosses. 



/Leaves without hyaline points 2 



\ Upper leaves with hyaline points 6 



/Cells long, very narrow ; stem with many short branches 4. fasciculare 



\ Cells shorter ; lateral branchlets few or none 3 



/Capsule round-ovate, hard ; Is. bistratose above 1. ellipticum 



~ \ Capsule longer ; Is. of one layer of cells 4 



{Ls. oblong, very obtuse, nerve not reaching the wide apex 2. aciculare 

 Ls. narrower, more tapering 5 



/Tall, loosely m atted ; without lateral branchlets .3. protensum 



^\Small, dense tufts ; usually with a few branchlets [var. of] 6. heterostichum 



cj Ls. with simply toothed hyaline points 7 



\ Hyaline points erose, and very rough with papilke 9 



/Branchlets absent ; capsule small, seta short 6*. sudeticum 



' \Plant with many lateral branchlets ; seta longer 8 



0/ Upper cells of ls. short, hair (in type) long 6. heterostichum 



\ Upper cells long and narrow .3. tamulosum 



/Ls. very papillose ; seta smooth 8. canescens 



"\Ls. smooth (except the hyaline points) ; seta rough 7. lanuginosum 



A. DRYPTODON. 



Stem dichotomous with .equal branches, without lateral 

 branchlets ; leaves obtuse, without hyaline points ; peristome 

 teeth resembling those of Grimmia. 



1. Rhacomitrium ellipticum B. & S. (Dicranum ellipticum 



Turn. ; Grimmia elliptica Am., Braithw. Br. M. Fl.) 



(Tab. XXIII. H.). 



Stems short, \-\\ inches high, in close, rigid tufts, brown, 

 fragile, naked at the base. Leaves patent, small, erect and rigid 

 when dry, solid, without hyaline points, shortly oblong-lanceolate , 

 widened just above the base, thence narrowed to a stout, rather 

 obtuse point, margin plane, or slightly recurved at the base ; 

 thickened above ; nerve distinct below, becoming narrower and 

 obscure above, brownish. Cells of the base elongate-linear, 

 strongly nodulose, incrassate ; only a single marginal row occa- 

 sionally rectangular and hyaline; above, in middle of leaf 

 becoming shorter and wider, about twice as long as broad, at the 



