192.")] SetcheU-Gardner: Melcmophyceae 509 



colorless cells with scanty chromatophores, and (:{) a cortical layer 

 of short, branched, closely compacted, erect filaments composed of 

 short, colored cells forming; a more or less smooth or wrinkled surface ; 

 zoosporangia, embedded within the thallus, more or less cylindrical, 

 becoming difform, usually attached laterally ; gametangia unknown. 



Xaegeli, in Kuetzing, Tab. Phyc, vol. 8, 1858, p. 2, pi. 3, fig. II. 



Comparison of Petrospongium Berkeleyi (Grew) Naeg. with Cylin~ 

 drocarpus microscopicus Crouan reveals such a difference in habit, 

 structure, etc., that it seems impossible to place the two species in the 

 same genus. We are also of the opinion that they belong in separate 

 families. The figures of Cylmdro carpus microscopicus, especially 

 those of Kuckuck (1899, p. 88, pi. 6, figs. 1-5) show a plant of definite 

 habit, growing in tufts (mucose, fide Crouan) rather tending to 

 elongate although only slightly so. without its individual branched 

 filaments being agglutinated into the definite thallus with inner 

 and outer distinct tissues as in the Leathesiaceae, but united into 

 a spongy (fide Kuckuck) mass by intertwining rhizoidal corticat- 

 ing filaments. We are inclined to place Cylindrocarpus micro- 

 scopicus in the Ectocarpaceae, as an extremely differentiated type 

 of such forms as Eetocarpus liemisphericus and E. chantransioid.es 

 and looking toward the iEgiraeeae and perhaps, also, the Leathe- 

 siaceae, but not properly of them or, to the same degree, differen- 

 tiated into definite inner transparent and outer colored layers. 

 Petrospongium Berkeleyi (Grev.) Naeg. and P. rugosum (Okamura) 

 S. and G., especially the latter, have their tissues differentiated and of 

 agglutinated, level-topped filaments and are, in our opinion, perfectly 

 typical members of the Leathesiaceae. 



Petrospongium rugosum (Okamura) S. and G. 



Plate 39, figs. 42, 43 



Thallus adhering more or less loosely to the substratum, circular to 

 irregular in outline, flat or thrown up into folds, more or less spongy 

 and lubricous, 2.5-5 cm. (up to 10 cm., cf. Okamura) diam., 1.5-2.5 

 mm. thick, of a dark, glossy, chestnut brown color ; cells of the cortical 

 layer 8-11//. diam., 1-2 times as long as the diameter ; zoosporangia 

 narrowly ellipsoidal, at times decidedly difform, attached laterally a 

 little below the middle and near the base of the cortical filaments, 

 75-90/x long, 16-22/x broad. 



Growing on rocks in the upper littoral belt exposed to surf. 

 Central and Southern California. 



