V. RIIODYMENIACE/E. 153 



nately decompouiKl. The pinnules are of two kinds ; the jnimary or lowest in 

 position arc generally simple, short, acute, either subulate or cultrate, and are set 

 distichously at alternate sides of the branch ; the secondary are pinnulate or pec- 

 tinato-decompound, and spring singly, or two, three, or four consecutively from 

 above the axil of their primary, in the space between its place and that of the next 

 primary at the opposite side of the stem. In this way, the ramuli throughout the 

 frond are alternately geminate, ternate, quaternate, etc. In one section of the 

 genus, peculiar to the southern hemisphere, the ramuli are geminate ; that is, each 

 primary subtends but one secondary ramulus ; in the other section, to which our 

 P. cocclnexiiH belongs, two or more secondaries are ranged above each primary. All 

 the species are remarkable for their brilliant colour. 



1. Plocamium coccineiim, Lyngb.; frond narrow, cartilaginous, piano-compressed, 

 decompound ; ramuli alternately ternate or quaternate, the lowest of each series 

 subulate, very entire, the upper pectinate on their upper edges ; conceptacles 

 marginal, solitary, sessile ; spore-leaves on the inner faces of the pectinate ramuli, 

 divaricately branched. Harv. Phyc. Brit. t. 44. J. Ag. Sp. Alcj. 2, jh 39-5. Kiltz. 

 Sp. Alg. p. 883. Fucus coccineus, Hiids. Turn. Hist. t. 59. P. Pot. t. 1242. 



Hab. San Francisco, California, Dr. Sinclair, Capt. Pike. Boston Bay, Miss 

 Eaichshurst. (v. v.) 



Captain Pike's specimen is about four inches high, a line broad, alternately and 

 distantly branched, the stem and branches two-edged, but not much compressed 

 below, flatter above. Branches decompound in their upper half Paniuli generally 

 alternately ternate or quaternate, the lowest ramulus subulate, about a line long, 

 the two above it elongate, compound in a similar order. Stichidia formed from 

 the ultimate ramuli of the upper divisions of the branches, palmate or dichoto- 

 mous, the divisions truncate. Colour a dark lake-red. Substance cartilaginous. 

 It imperfectly adheres to paper. 



The rarity of Plocamium coccineum on the eastern shores of North America is 

 very remarkable, considering that it is common on the Atlantic shores of Europe, 

 and throughout a very wide extent of the Southern Ocean. The Californian 

 specimen above described is more robust, more cartilaginous, and less compressed 

 than any that I possess from other quarters, but ofll^rs no peculiarity of ramifica- 

 tion by which it can be distinguished. 



V. RHABDONTA. Hai^. 



Frond terete, decompound, somewhat tubular ; tube partially filled with longitu- 

 dinal, branching and anastomosing filaments ; the peripheric stratum composed of 



VOL. IV. — ART 5. ^ 



