V. RHODYMENIACE.E. 151 



at the margin ; conceptacles spherical, marginal ; tetrasporcs contained in the 

 thickened tips of the lacinia;. /. Ag. Sp. Ahj. 2, p. 385. Rhodijmmia eristata, 

 Grev. — Harv. Phyc. Brit. t. 30?. Callophi/llis eristata, Kutz. Sp. Alg. p. 747. Fucus 

 cristatus, L. — Turn. Hist. t. 23. 



Hab. Arctic coast, Lieut. W. N. Griffiths, R. JSf. Abundant from Halifax 

 ( W. H. H.) to Cape Cod, many varieties, Mrs. Asa Gray, Mrs. Mudge, Dr. Durkee, 

 &c. (v. V.) 



Frond one to tliree inches high, distichous, excessively branched, more or less 

 fastigiate, flabelliform, the expansion of the branches equal to the length of the 

 frond. Branches linear, varying in breadth from the diameter of a hog's bristle to 

 one or two lines or more, sub-dichotomously, palmately, or alternately decompound, 

 the divisions successively naiTowed. Sometimes the whole frond is sub-dichoto- 

 mous and nearly equally narrow ; sometimes decompound-pinnate, and sometimes 

 a few broad, pinnatifid laciniae are bordered by finely-cut ramuli. The frond is not 

 perfectly flat, when narrow, but two edged, slightly convex in the centre. Concep 

 tacks abundant, spherical, marginal, as large as poppy seed, dark coloured. Tctra- 

 spores cruciate, thickly congregated in the thickened and dark coloured tips of the 

 lacinife. Colour a beautiful crimson lake, becoming scarlet on steeping in fresh 

 water. Substance somewhat cartilaginous. It shrinks in drying, and but imper- 

 fectly adheres to paper. 



Most of my Halifax specimens are of the narrow varieties, some so narrow and 

 multifid as closely to resemble the smaller and slenderer forms of Plocamium coc- 

 cineum. In Boston Bay, where the plant occurs in great profusion and beauty, 

 broad and narrow varieties are nearly equally common. The geographic range of 

 this species is alluded to in our Introd. p. 23. 



III. RHODOPHYLLIS. Kutz. 



Frond flat, membranaceous, dichotomously cleft, often with marginal lobes, com- 

 posed of two strata of cells: cells polygonal, those of the medullary stratum larger, 

 longitudinal ; of the outer, vertical, in few rows. ConcejMcles mostly marginal, 

 sub-spherical, with a closed pericarp (composed externally of radiating, internally 

 of concentrically arranged cellules) ; sporiferous filaments very numerous, radiat- 

 ing from a basal placenta ; the fertile ones forming roundish masses of spores from 

 the uppermost cells. Tetraspores zonate, immersed in the frond or in its marginal 

 lobes. 



A small genus typified by lihodymenia bifida, Grev. (Fuctis bifidus, Turn.), and 



