118 GELIDIACEyE. v. 



ones short, subulate, acute, simple, the upper longer and once or twice compounded 

 with similar pinnules. All the pinnules are acute, more or less constricted at their 

 insertion, and many of them denticulate at the mai'gin or set with distichous, 

 tooth-like ramuli, which probably afterwards lengthen into pinnules. The fertile 

 pinnules (containing tetraspores) are incrassated in the middle, spindle-shaped, and 

 very generally furnished with marginal spine-like processes. Colour a very dark, 

 blackish purple. Substance rigid, horny when dry. It does not adhere to paper. 



In aspect this plant is most like G. spinulosum, J. Ag., but the fertile ramuli are 

 very different. 



II. EUCHEUMA. J. Ag. 



Frond terete or piano-compressed, carnoso-cartilaginous, horny when dry, decom- 

 pound, usually spiny or tuberculated, solid, composed of three strata ; the medullary 

 stratum, of densely interwoven, elongated, anastomosing longitudinal filaments ; 

 the intermediate^ of several layers of roundish-angular cells, gradually smaller 

 outwards ; the cortical, of minute, coloured cellules set in radiating filaments, at 

 right angles to the axis. Conceptacles ovate, sessile on the ramuli, furnished with a 

 terminal pore, containing within a very thick pericarp a central, fleshy pilacenta 

 suspended within the cavity, and attached by numerous confervoid filaments to the 

 walls ; spore-threads simple or branched, issuing from all sides of the placenta, 

 moniliform, three or four roundish, oblong, or sub-pyriform spores formed in each 

 thread. Placenta often hollow. Tetraspores immersed in the cortical stratum, 

 scattered, zonate. 



This genus is formed, by Prof. J. Agardh, for several tropical or sub-tropical Algae 

 with shrub-like, robust, cartilagineo-corneous, mostly spinous, tuberculated fronds. 

 They were formerly placed either in Sphcerococcus, Gracilaria, Hypnea or Gigartina, 

 from all which genera, as now understood, they differ in structui"e and fructifica- 

 tion. The conceptacles, however, are only known with certainty in our American 

 species, and have a structure in some respects connecting the Sp>hcerococcoidew 

 (among which Prof. Agardh now arranges this genus) and the Gelidiacece, as here 

 defined. To me the placentation appears so similar to that of Solieria that I am 

 unwilling to separate these genera widely; while I admit that the moniliform 

 spore-threads show an affinity with Gracilaria. 



1. EucHEUMA isiforme, J. Ag.; frond fruticose, very robust, decompound, much 

 branched; branches spreading to all sides, the lesser branches often opposite or 



