V. HELMINTnOCLADE.E. 131 



11 AB. On corals, &c. at Key West, IT. 11. 11. (v. v.) 



Fronds from half an inch to an incli in diameter, delicately membranaceous, 

 orbicular or reniform, closely applied by the whole inferior surface to the object 

 on which they grow, and to which they are attached by minute rootlets, freely 

 emitted from the membrane. Upper surface finely striate, the striaj radiating 

 from the centre to the circumference, composed of hexagonal, seriated cells. Mar- 

 gin circumscribed, flat. Colour toward the centre of the frond dark-red brown, 

 paler and redder toward the margin. I have not seen fruit on the American spe- 

 cimens, which in other respects closely resemble those from the ^\''est of Ireland. 



2. Petssonnelia imbricata, Kiitz. ; " depressed, adnate, red-black, coriaceou?!, 

 irregularly sub-orbicular, lobed, imbricated, rugose, the lobes rounded." Kiitz. Sp. 

 Alg.p. G94. 



Hab. Newfoundland, Lenormand, fide KUtzing. 



Order YIII. HELMINTH0CL.4DE^. 



Helminthodadecc, J. Ag. Sp. Gen. and Ord. Alg. %p. 410. Part of Cryptommeoe, 

 J. Ag. Alg. Medit. p. 81. Harv. Man. Ed. 2, p. 131. 



Diagnosis. Gelatinous, or gelatino-membranaceous, rosy or purple (cylindrical) 

 sea-weeds, almost wholly composed of confervoid filaments set in loose gelatine. 

 Sporiferous-nuclms immersed in the frond, destitute of pericarp, spherical, formed 

 of branching spore-threads radiating from a central point, and bearing minute, 

 roundish spores. 



Natural Character. Root discoid, little developed. Fronds cylindrical or com- 

 pressed, rarely somewhat flattened, dichotomous, pinnate, or shrub-like, ^ometimos 

 very mucli branched, composed wholly or in great part of slender cylindrical or 

 moniliform filaments variously combined together and lying in a transparent gela- 

 tine of greater or less consistence. The axis of the frond is in all cases formed of 

 a bundle of longitudinal threads, interlaced together and frequently anastomosing, 

 generally compactly united by a rather tenacious gelatine, and giving off, on the 

 outside of the bundle, numerous horizontal filaments whith terminate in those of 



s -2 



