V. IIHODOMELACE.E. 15 



articulated, polysiphonous. Ramuli alternate, subulate, acute, transversely striate. 

 Conceptacks inflated, solitary, Avith contracted and produced apertures, containing 

 within a membranous pericarp a tuft of pear-shaped spores on simple funiculi, 

 radiating from a basal placenta. Tetraspores tripartite, lodged in axillary, tufted, 

 lanceolate receptacles {stichidia), irregularly seriated. 



As revised by J. Agardh (Linnrea, vol. XV. p. 28.), this genus is nearly related 

 to Acanthophora on the one hand, and to Rhodomela on the other. The species are 

 all from the warmer parts of the ocean. I have seen only the conceptacks o{ A. 

 Seaforthii and A. Blodgettii ; and only the stichidia of A. triangulare. 



1. Alsidium triangulare, J. Ag. ; frond triquetrous, between dichotomous and 

 pinnate, much branched ; branches alternate or secund, closely set throughout with 

 minute, trifarious, bifid, tritid or multitid ramuli ; stichidia axillary, tufted. J. 

 Ag. in Linncea XV. p. 28. Bryothamniontriangidare, Kiitz. Sp. Alg. p. 842. Phys- 

 cophora triangularis, Kiitz. Phyc. Gen. p. 434. t. 51. jig. 1. Thamnopliora triangularis, 

 Ag. Syst. Alg. p. 240. (Tab. XIII. A.) 



Hab. Abundantly thrown up at Key West. (A common West Indian 

 species), (v. v.) 



Frond C-12 inches long or more, excessively branched. Stem cartilaginous, 

 cylindrical below, where it is frequently two lines in diameter, gradually becoming 

 narrower and more compressed upwards, forking repeatedly and then irregularly 

 divided. Branches scattered, triangular, with a flabelliform outline, much divided; 

 the lesser branches alternate or secund, having shorter branchlets toward the apices. 

 All the younger parts of the frond are set, at distances of a line or two, with 

 minute, trifarious, mostly three pronged ramuli, not a line in length: these, as well 

 as the younger part of the branches, appear transversely striate when examined with 

 a pocket lens. Conceptacks I have not seen. Stichidia densely tufted in the axils 

 of the trifid ramuli, distorted, more or less fusiform, tapering to a point, each con- 

 taining tlu'ce or four large tetraspores in an imperfect line. A cross section of the 

 frond shows a small axial cell surrounded by eight priinary cells (or siphons), out- 

 side which are several rows of irregularly polygonal cells, Avhich diminish in size to 

 the circumference. The surface cellules are very minute, so that the branches 

 appear opaque and inarticulate. Colour when fresh a clear purplish pink, soon 

 fadinjr in the sun, and becoming reddish brown in the herbarium. Substance carti- 

 laginous, very tough, and not in the least adhering to paper in drying. 



Plate XIII. A. — Fig. 1. A small plant of Alsidiuji triangulare; the natural size. 

 Fig. 2, apex of a branch with three-pronged ramuli ; ^(7. 3, tuft of stichidia containing 

 tetraspores, removed from the axil of a ramnlus ; fig. 4, a transverse section of the 

 frond ; — the latter figures more or less highly magnified. 



