V. CERAMIACE.E. 211 



Ag. It is much more opaque than that species, with a smaller axial tube and 

 shorter articulations, and the ramification is as orderly as in Plocamium coccineum. 



CENTROCERAS. Kiifz. 



Frond filiform, dichotomous, articulated, corticated with oblong cells, arranged 

 round the internode in longitudinal lines. Favellce sessile on the branches, sub- 

 tended by a few involucral ramuli, and containing, within a hyaline periderm, many 

 angular spores. Tetraspores formed by a transformation of some of the cortical 

 cells, projecting from the surface, roundish, triangularly divided. 



Plants with the external habit of Ceramium, from which genus this chiefly diff'ers 

 in having the cells of the cortical layer arranged in longitudinal, striteform rows, 

 instead of being irregularly placed. Of the following species, which has many 

 varieties, and is dispersed very widely through the Atlantic and Pacific Oceans, 

 Prof Kutzing has made no less than eight species. 



1. Centroceras davtdatu77i, Ag. ; frond capillaiy, rigid, dichotomous, fastigiate, 

 at length proliferous from the axils ; apices hooked inwards, lower internodes four 

 to six times as long as broad, upper successively shorter ; nodes armed with a whorl 

 of minute spines ; tetraspores whorled round the nodes of the lesser branches and 

 ramuli ; favelloe geminate, involucrate. J. Ag. Sp. Alg. 2, p. 149. Centroceras sp. 

 omnes, Kiltz. Sp. Alg. 688. (Tab. XXXIII. C.) /3 erispulum, Mont. ; filaments 

 variously curved and twisted, and beset with lateral, squarrose ramuli, 3Iont. Cuba, 

 t. 2,/. 1. 



Hab. Abundant at Key West, on rocks, on the foundations of the Fort and else- 

 where near low water mark, W. H. H. (both varieties), Prof. Tuomeg, &c. (v. v.) 



Fronds densely tufted, two to four inches long, as thick as human hair, nearly 

 of the same diameter throughout, repeatedly and regularly dichotomous, the apices 

 fastigiate ; branches straight and erect in var. a, variously twisted and spreading 

 in ^, naked, or furnished with lateral, proliferous, forked branchlets, which spring 

 either from any node along the stem or often from the axils, especially the upper 

 ones. Frond articulated to the base ; the internodes in the lower part several times 

 longer than broad, shorter above and very short towards the ends of the ramuli, 

 coated with cells arranged in longitudinal striosform lines ; the cellules toward the 

 apex of each internode short, quadrate, gradually longer toward the base, and 



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