THE GREEN AI.GAE OF NORTH AMERICA 57 



P. 219, for No. i of Key to the Species of Prasiola, substitute, 



i. Marine. ia. 



i. Fresh water or terrestrial. 2. 



ia. Frond 33-45 /* thick, with or without stipe. 4. P. borealis. 



ia. Frond 10-15 fj. thick, with long distinct stipe. 6. P. stipitata. 



P. 221, after account of P. CRISPA, add, 



6. P. STIPITATA Suhr in Jessen, 1848, p. 16, PI. Ill, figs. 

 11-16; I. F. L/ewis, 1916, p. 90, figs. 1-2. Fronds tufted, sev- 

 eral from the same base, stipe long, slender, at extreme base of 

 only a single series of cells, widening and increasing in number 

 of cells, finally expanding into a cordate-cuneate frond, up to 

 5 mm. long. Cells of frond, before dividing, 6-io/x square, in 

 quite regular and distinct square areas ; cells in stipe larger 

 and more distant, in regular longitudinal and transverse series, 

 but not forming areas. In dense masses on rocks at high tide. 

 Woods Hole, Mass., I. F. Lewis. Europe. 



Page 221, after the generic description of GAVEI^A, insert, 



KEY TO THE SPECIES OF GAYEHA. 

 i. Fronds with deep regular constrictions and n6 rhizoids. 



2. G. constricta. 

 i. Fronds cylindrical or somewhat irregular, with abundant rhizoids. 



i. G.polyrhiza. 



In description of G. POLYRHIZA, change "parietal " to read 

 "stellate" chromatophores. 



Page 222, after account of G. POLYRHIZA, add, 



2. G. CONSTRICTA Setchell & Gardner in Gardner, 1917, 

 p. 384, PI. XXXII, fig. 5 ; XXXIII, figs. 5-9. Frond similar 

 to that of G. polyrhiza, but curved and uncinate, and with fre- 

 quent deep constrictions at fairly regular intervals, each con- 

 striction caused by the failure of a certain group of primary 

 cells, usually 2-6 in a group, to divide vertically. A few very 

 slight rhizoidal projections at the extreme base, no other rhi- 

 zoids ; primary filament about 2o//.diam., upper part of frond 

 up to 150 jt*, intervals between constrictions 200 p. to i mm. 

 Cal., N. Iy. Gardner. 



This new species, quite distinct from G. polyrhiza, certainly 

 supports the validity of the genus. Prasiola borealis grows in 

 the neighborhood, but no intermediate forms have been found. 

 It seems to be a case where the conditions that favor Prasiola 

 favor also the nearly related Gayella. 



