CB1 PTONEM I a i BJE. 121 



Porcellaria Lumbricalis, Lamour. Fucus fastigiatus, Hud*. V. 



Lumbricalis, Gm. K. furcellatus, Linn. 

 llah. On submarine rocks, within tide-marks, generally growing 



in tidal pools. Perennial, Winter. Common. 

 There is such a strong externa] resemblance bei 

 this and the preceding Bpe< ies, thai they are often mist 

 one for the other, and without contrasl ing the fibrous 

 of the former with the large Bcutate base of the latter, 

 it might, in some instances, be difficult to discriminate 

 between them. There is, indeed, some difference in the 

 structure of the frond, but not of a very striking character, 

 and, though easily observed when slices of both are 

 together under the microscope, most difficult of bei 

 fined in intelligible words. And yet, \\ ith this resemblance 

 in genera] appearance, all modern authors, with th 

 ception of Kutzing, place them in different genera, and, 

 until very lately, even in different families. Dr. Caspary 

 has given, in the * Annals of Natural History " (Second 

 3, vol. vi. p. 87), a minute account of the compara- 

 tive structure of Furcellaria and Poh/ides, with micro- 

 metric measurements of the cells composing the various 

 strata oi' their fronds. 



LXVIII. DUMONTIA. 



20S. filiformis {The thread-like Dumontia) \ frond undivided, 

 attenuated to each extremity, pinnated with long, simple, 

 tapering branches, Oreo. Alg. JBrit.p. 165. t. 17. (Ai 

 PL X1A1. Fig. 209.) 

 Dumontia incrassata, Lam. Ualymenia filiformis, Ag, Ghondria 

 purpurascens, Qrev. Gtatridium filiforme, Lyngb. I 

 i filiformis, Fl. Dan, Diva filiformis, Wahl. 

 Hob. On reek- and Btones in the sea, at half-tide level. Annual. 

 Summer. j8. in plaoi - i Loosed to tidal currents. Common* 

 A very common plant, and one which, though tolerably 

 at to a particular ramification, having Long Bimple 

 branches springing from a simple Btem, is yet subject to 

 many modifying causes, which affect its habit and general 

 appearance very considerably. In one variety the frond 



is often an inch in diameter, and BO much puckered ami 



waved, that, except in colour, it strongly resembles /.' 

 morpha intestinalis. Vet this variation appears to 

 solely from Locality, being always found where a - 



stream rolls dow n. 



