340 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



Fronds 10-20 cm. high, light green; main filaments 80-120 /u. 

 diam., regular!}' flexuous, with flexuous alternate branches, 

 40-80 p. diam., with alternate or secund, curved and sometimes 

 refracted raniuli ; cells from 6 diam. long below to 2 in the 

 ramuli. Newfoundland to Bermuda and Florida, Alaska. 



Europe. 



A plant of nearly the same range on the Atlantic as C. glau- 

 cescens ; it will probably be found on the Pacific to the south of 

 Alaska. It occurs in rock pools, but usually near low water 

 mark, and generally in colder places than C. glaucescens. 

 It is a firmer plant, larger in all dimensions except total length of 

 frond, and is distinctly flexuous throughout. On the other 

 hand the larger forms of this species approach small forms of C. 

 gracilis, C. hirta, and C. laetcvirens^ and it is often difficult to 

 draw the line. Typical C. gracilis has long secund ramuli pec- 

 tinately arranged at the end of every branch ; C. hirta has 

 rather shorter ramuli in secund series all along the filaments; 

 C. laetcvirens has short, stout ramuli in dense fascicles at the 

 tip. By these characters normal forms can be distinguished 

 without much difficulty. C.flcxuosa Vickers, 1908, p. 19, PI. 

 XV, is hardly our plant ; the figure is rather like a slender 

 form of C. gracilis. 



Forma DENSA Collins, 1902, p. 121 ; P. B.-A., No. 979. 

 Branching of all orders very dense ; texture of frond spongy. 

 At lower limit of literal zone. Newport, R. I. 



Habit like C. albida, but form and dimensions of cells like C. 

 flexuosa. 



15. C. CRUCIGERA Grunow, 1867, p. 38. Fronds stout, 

 pale green, rather loose, sparingly dichotomously branched ; 

 branches patent, connate for a short distance at the base ; 

 ramuli scattered, short, of few cells, alternate or oftener oppo- 

 site, very patent ; cells about 300 /u. diam. below, 6-8 diam. long ; 

 ramuli 75-110 p., 3-4 diam. long, somewhat constricted at the 

 nodes. Guadeloupe. 



Grunow's description has been copied ; he considers this a 

 very distinct species, not to be mistaken for anything else. 



16. C. EXPANSA (Mert.) Ktitzing, 1853, PI. XCIX ; Farlow, 

 1881, p. 55; P. B.-A., Nos. 121, 977, 1280. Fronds dull green, 

 loosely branched, main branches 100-150 p diam., flexuous, 

 with smaller, patent, secondary branches, divaricately divided ; 



