Howe : Phycoi.ogical studies 245 



prolifications sometimes 10-20 times as long; wall of filament 

 conspicuously lamellate, 15-70/i thick (including the enclosed, 

 usually thinner wall of the individual cell) ; upper face of the 

 diaphragms often strongly mammillose or tuberculose with lam- 

 ellate elevations, these 30-50/^ broad: filaments sometimes co- 

 herent or concrescent at points of casual contact by means of 

 small, usually oval or quadrate, fibular cells : ordinary cells 

 often forming cysts, either as a whole or after endogenous division 

 (Plates 13 and 14). 



Siplionocladns rigidus occurs in southern Florida and in the 

 Bahama Islands, growing in water that is from 3 to 10 dm. deep 

 at low tide, often in association with GoniolitJion strict 11m Foslie. 

 It is crisp and rigid when living, crunching under the collector's 

 boot in the water somewhat like the GoniolitJion whose society it 

 affects. As is common in the family to which it belongs, the 

 dried specimens give a poor idea of the living habit of the plant. 

 Our no. /507 from Key West, Florida (October ^o, 1902), from 

 which the material used for the published photograph and for 

 most of the drawings was taken, we consider the nomenclatorial 

 type. Specimens collected under this number were distributed in 

 the Phycotheca Boreali- Americana as no. ioji under the name 

 Siplionocladns tropicus (Crouan) J. Ag. 



Siphonocladus rigidus is probably more nearly related to Siplio- 

 nocladns bracJiyartms Svedelius,* from Magellan's Straits, than to 

 any other described species, but 6". rigidus is larger and coarser, 

 the filaments measuring 350-11 50 a in thickness, while those of 

 5. brachyartrus are given as but 200-300 ft, the cells are mostly 

 even shorter proportionally than in S. brachyartrus, and the branch- 

 ing is more often and more truly dichotomous. 



Siplionocladns rigidus is allied also to 6". tropicus (Crouan) 

 J. Ag., yet is sufficiently distinct as may be gathered from a com- 

 parison of our photograph of a fluid-preserved specimen ( pl. ij, 

 f. /) with the photograph (pl. ij, f. 2) of the dried specimen in 

 hb. Agardh, which was communicated by M. Maze as "Apjohnia 

 tropica Crouan " and may fairly be considered the type of the species, 

 inasmuch as J. Agardh was the first (Till. Alg. Syst. 5 : 105. 1887) 

 really to publish a description of it. The specimens from Florida, 

 Barbados, and Mauritius, also cited by J. Agardh as belonging to 



*Svenska Exped. till Magellanslandema, 3 : 304. /. j and />/. /<?. 1900. 



