V. SPHiEROCOCCOIDE^. 97 



leaflets are as blunt as those of D. ruscifoUa. Both varieties accompany the oi'dinary 

 form in Charleston Harbour, the most northerly station hitherto ascertained for D. 

 Hypoglossum in America. 



9. Delesseria tcnuifoUa; frond filmy, pale rose-red, broadly linear, obtuse, flat, 

 repeatedly proliferous from the capillary, articulated midrib with leaflets of similar 

 form; at length much branched, fastigiate. (Tab. XXII. B.) 



Hab. At Key West, Feb. 1850, IF. H. H. (v. v.) 



Frond originating in a linear, obtuse, perfectly flat leaf, one or two inches long 

 and about two lines in breadth, of extreme tenuity, and furnished with a percurrent, 

 articulated midrib composed of a triple row of cells, of which tlie central cell is 

 cylindrical and more deeply coloured, the border cells half-hexagonal ; the three 

 cells taken together forming a hexagonal areole or articulation of the midrib. This 

 primary leaf emits others from its midrib, and the process is repeated till there 

 results a much branched, fastigiate, globose frond, whose lower branches (the de- 

 nuded midribs of the primary leaves) are thickened to the diameter of a hog's 

 bristle. I have not seen conceptades. Tefmspores occur in very small sori placed 

 one at each side of the midrib near the tips of the young leaves. The substance of 

 the membrane is exceedingly thin and semi-transparent. The cellules toward the 

 midrib are large and polygonal, not regularly hexagonal, but nearly so; those 

 toward the margin ol)long or cylindrical, disposed in lines at an angle of 45° with 

 the midrib. Colour very pale. In drying, it adheres most closely to paper. 



Thin and delicate as are the leaves of D. Hypoglossum, those of the present species 

 are much more so, and, wdien dry, appear as a mere glossy film on the surface of 

 the paper. Under the microscope, it is easily known from D. Hypoglossum. by the 

 structure of the midrib, and the disposition of the cellules of the membrane, while 

 its pale colour and extreme tenuity sufficiently mark it to the naked eye. In the 

 form of the leaf it resembles D. ruscifoUa, but in other respects abundantly differs 

 from that strong-growing species. 



Plate XXIT. B. Fig. 1, Delesseria tenuifolia, the natural size. Fig. 2, some 

 leaves, with sori in their apices ; fig. 3. apex of a leaf enlarged to show the structure 

 of the membrane ; fi{/. 4, a tetraspore ; — all magnified. 



10. Delesseria involvens ; frond filmy, pale rose-red, linear-lanceolate, attenuate, 

 having the apex strongly involute, bordered with oblique bullate undulations 

 repeatedly proliferous from the articulated midrib with leaflets of similar form ; at 

 length much branched and fastigiate. (Tab. XXII. A.) 



Hab. At Key West, Feb. 1850, TI". H. H, Dr. Blodgett. (v. v.) 



The mode of composition of the frond is the same as in the last species ; a pri- 



VOL. IV. — AET. 5. ^ 



