THE GREEN ALGAE OF NORTH AMERICA 387 



the size of the utricles, which varies within quite wide limits. 

 It is probable that when the genus is thoroughly studied, pres- 

 ent arrangements will be considerably changed. 



KEY TO THE SPECIES OF CODIUM. 



i. Forming a continuous expanded incrustation. 2. 



i. Not forming a continuous expanded incrustation. 3. 



2. Utricles usually 50-60 n, rarely 100 /u diam. i. C. adhaerens. 



2. Utricles usually 125-200 fj., rarely 300 ^ diam. 2. C. difformc. 

 3. Frond globose to pyriforru. 3. C. Ritteri. 



3. Frond branched, cylindrical or compressed. 4. 



4. Frond creeping, attached by holdfasts. 4. C. repens. 



4. Frond erect. 5. 



5. All or part of the utricles rnucrouate. 9. C. mucronatum. 



5. Utricles blunt, smooth. 6. 



6. Branches usually constricted at base. 6. C. isthmocladum. 



6. Branches not usually constricted at base. 7. 



7. Frond normally cylindrical throughout; utricles seldom 200 fj. diam. 



5. C. tomentosuin. 

 7. Frond normally more or less compressed. 8. 



8. Utricles usually 400 /j. diam. or more. 7. C. elongatuui. 



8. Utricles usual 1}- less than 250 /j.. 8. C. Lindenbergii, 



1. C. ADHAERENS (Cabr.) Agardh, 1822, p. 457 ; Harvey, 

 1846-51, PL XXXV. A; P. B.-A., No. 523. Forming an ex- 

 panded, incrusting layer, closely adherent to the substratum, 

 dark green, lubricous, increasing by marginal growth, with 

 rounded lobes ; the filaments and utricles united by firm gela- 

 tine ; utricles clavate, 50-60, rarely ioO|udiam., sometimes with 

 long, cylindrical lower part. On exposed rocks. Vancouver to 

 Cal. Europe, Asia, Occanica. 



Forming a firm crust, about i cm. thick, on rocks ; quite dis- 

 tinct from our other species, except C. difformc, which has a 

 similar habit, but larger utricles. 



2. C. DIFFORME Kutzillg, 1843, p. 300; 1856, PI. XXXV, 



fig. 99 ; Vickers, 1908, p. 22, PI. XXV. Habit like that of C. 

 adhaerens; utricles 125-200, rarely up to 300 /j. diam. Fla., 

 W. I. Mediterranean, warmer Atlantic, Pacific. 



Apparently a plant of wanner waters, while C. adhaerens ex- 

 tends considerably farther north. 



3. C. RITTERI Setchell and Gardner, 1903, p. 231, PI. XVII. 

 Frond globose to pyriform, up to 3 cm. high, attached by a dis- 

 tinct stipe-like base, solid, the center consisting of a felt-like mass 

 of fine filaments; utricles pyriform, blunt, 1.50-400 //, diam. 

 older ones usually swollen in the middle, and with the mem- 



