1 16 SYNOPSIS OF BRITISH SEAWEEDS. 



Phlebothamnioo arbuscula, Ktz* Dasya spongiosa, Ag. Con- 

 ferva arbuscula, R. Br, 

 Abundant on the western Bhoree of Scotland and Ireland : 

 stem. On rocks and mussel-sheila, near low- 

 water mark, usually in places Kit bare on the recess of the 

 tide; also in tide-pools. PerenniaL Summer and autumn 

 The most robust and bushy of all the British ( 'nlHthum- 

 . and therefore well named Arbuscula. The main stem 

 is often upwards of a line in diameter, and divided into 

 several stout branches, densely clothed with finely divided 

 ramuli. The colour is always very dark, varying from 

 brownish to a more or less vivid vinous purple. No spe- 

 cies can well be confounded with the present, except, 

 perhaps, very luxuriant specimens of C. spongiosum, but 

 the microscopic characters of that species are extremely 

 different. 



256. Brodiaei (Brodie's CaUithamnion); stem sub-opaque, veiny, 

 obscurely jointed, slender, simple, furnished throughout with 

 densely inserted, patent, lateral branches ; branches fur- 

 nished at each joint with short, quadrifarious, secondary 

 branches with a narrow hastate outline ; plumules alternate, 

 subsimple, pinnate, ovate, then* pinnules patent, frequently 

 with a few secund processes near the apex ; tetraspores 

 oval, sessile near the tips of the pinnules, or on their acces- 

 sorv processes ; favellae bilobed, on the secondary branches, 

 Harv. in Hook. Br. Fl. v. 2. p. 105. (Atlas, PI. LVI. 

 Fig. 257.) 

 Hob. Parasitical on Alga?, near low-water mark. Annual. 

 Summer. Rare. 

 Cal. Brodicei has much the habit of a small specimen of 

 C. tetragonum ; the conical outline, undivided shrubby 

 stem, and lateral branches, are common to both. But the 

 microscopic characters show a much nearer affinity with 

 C. Hookeri, to some varieties of which it makes a very near 

 approach. In the individuals producing tetraspores, which 

 are always more slender and more regularly branched 

 than those which bear favella, the pinnules are pretty 

 constantly furnished with short, secund ramuli in their 

 upper half. In C. Hookeri such ramuli are either absent 

 or are alternate, and more patent. In the length of the 

 joints there is not much difference, and both species have 

 sub-opaque stems, traversed by densely packed articulated 



