THE MARINE ALG^E OP NEW ENGLAND. 189 



Fronds parenchymatous below, but above formed of loosely united 

 filaments, tetraspores formed in the filaments Petrocelis. 



52. Fronds tubular , 53 



Fronds filamentous . 54 



Fronds membranaceous 75 



53. Fronds cartilaginous, hollow throughout, rigid, proliferous, tetra- 



spores cruciate Halosaccion. 



Fronds slender, much contracted at the joints, but without dia- 

 phragms, tetraspores tripartite in depressed cavities . . Lomentaria. 



Fronds slender, nodose, with diaphragms at the nodes, tetraspores 

 tripartite in the cortical layer Champia. 



54. Fronds monosiphonous, without proper cortex 55 



Fronds with distinct axial and cortical layers 62 



55. Fronds monosiphonous throughout 56 



Fronds at first monosiphonous, becoming polysiphonous above, 



spores formed by divisions of any of the -cells, filaments simple, 

 gelatinous, dark purple '. Bangia. 



Fronds monosiphonous above, but below with a false cortex formed 

 by descending filaments given off from the cells 60 



Fronds formed of large cells placed end to end, with bands of smaller 

 cells at the nodes, in some cases the nodal cells extending in a 

 thin layer over the internodal cells 61 



56. Spores (as far as known) formed directly from the contents of any 



of the cells 57 



Spores on short pedicels, distinct, undivided TrentepohJia (?). 



Tetraspores and cystoearps present 58 



57. Filaments simple, forming a fine web over other algae. 



Erythrotrichia. 

 Filaments dichotomously branching, minutely tufted. . Goniotrichum. 



58. Fronds formed of prostrate filaments, from which arise erect pinnate 



filaments, cystoearps terminal, involucrate, spores irregularly 

 grouped, not surrounded by a common gelatinous envelope when 



mature Spermathamnion. 



Cystoearps terminal or lateral, spores irregularly grouped at ma- 

 turity, covered by a general gelatinous envelope 59 



59. Fronds dichotomous, formed of delicate vesicular cells, tetraspores 



in whorls at the joints, involucrate =. Griffithma. 



Fronds dichotomous or pinnate, tetraspores scattered on the 

 branches, solitary or aggregated, cystoearps lateral, usually bi- 

 nate Callithaimiion, in part. 



Fronds with a monosiphonous axis, nearly concealed by the densely 

 whorled branches, cystoearps terminal on short branches, tetra- 

 spores in whorls one above another on special branches . . Halurus. 



60. Fronds capillary or bushy, densely branching, cortications confined 



to tbe larger branches, and evidently formed of vein-like descend- 

 ing filaments CaUithamnion, in part. 



