THE GREEN ALGAE OF NORTH AMERICA 375 



tropicus, Howe's figures of S. rigidus would seem to be inter- 

 preted best as representing a development by "cysts," much 

 as in the former species. There is little doubt of the distinct- 

 ness from S. tropicus, but the relations in this direction are cer- 

 tainly closer than those with Cladophoropsis membranaceus . 

 It is at least probable that the lateral branches in Howe, PI. 

 XIV, fig. 2, correspond to the branches in Borgesen, fig. 4 ; and 

 that the frond originates in a similar, somewhat clavate cell. 



4. PETROSIPHON Howe, 1905, p. 248. 



Filaments united to form a disk, somewhat calcified, firmly 

 attached to the substratum, and piercing the same by rhizoids ; 

 disk monostromatic at the margin, polystromatic elsewhere, the 

 center often of short, erect filaments ; asexual reproduction by 

 aplanospores. 



P. ADHAERENS Howe, 1905, p. 248, PI. XV. Disks light 

 green, 2-6 cm. diam., orbicular or irregular, closely approxi- 

 mate ; margin striate ; up to 5111111. thick at the center; hori- 

 zontal filaments 300-850 /j. diam., straight or geniculate, dichoto- 

 mous ; cells ^2-20 diam. long ; rhizoids very abundant, pene- 

 trating the substratum ; aplanospores varying in size and form. 

 Bahamas. 



In characters of filaments, etc., like Siphonoclctdus, but differ- 

 ing by the definite disk-shaped frond, and the incrustation ; it 

 is closely adherent to the rock on which it grows. 



5. CHAMAEDORIS Montague, 1842, p. 261 

 Frond erect, with firm, clavate stipe, attached by rhizoids at 

 the base, and bearing a dense tuft of branching, articulate fila- 

 ments at the tip ; stipe monosiphonous, with closely set, annular 

 constrictions, much calcified. 



C. ANNUI,ATA (Lamarck) Montagne, 1842, p. 261 : Harvey, 

 1858, p. 43, PI. XIvII.B ; Vickers, 1908, p. 22, PI. XXIV ; P. 

 B.-A., No. 629. The only species ; stipe up to 10 cm. high; 

 head 2-3 cm. diam. Fig. 136. Fla., W. I. 



Africa, So. America, Indian Ocean. 



. The mop-shaped fronds are not to be mistaken. 



6. STRUVEA Sender, 1845, p. 49. 



Frond attached below by multicellular branched rhizoids ; 

 stipe simple or branched, monosiphonous, bearing one or more 

 flabelliform, net-like expansions, consisting of articulate, pin- 

 natel} 7 branched filaments, the tips of the branches attaching 



