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



of which issue in all directions, free, dichotomously branched 

 filaments, inarticulate but with occasional constrictions ; base a 

 mass of rhizoids ; reproduction unknown. 



The characteristic brush-like form in the species of this genus 

 easily distinguishes them from all our other algae except Rhipo- 

 ccphalus ; in the latter the filaments are united into many fan-like 

 expansions, while in Penicillus they are free, and issue in all 

 directions ; the species, however, are not very strongly marked, 

 and it is often a matter of difficulty to decide to which of them a 

 specimen is to be referred. 



KEY TO THE SPECIES OF PENICIIJ < US. 

 i. Filaments stout but relatively scanty ; stipe soft. 



3. P. Lamourou.vii. 



i. Filaments of moderate size, abundant ; stipe firm. 2. 



2. Stipe stout and short ; head pyriform. 4. P. pyriformis. 



2. Stipe longer ; head rounded. 3. 



3. Stipe slender, smooth ; filaments much calcified, i. P. capitatus, 



3. Stipe stout, rough ; filaments slightly calcified. 2. P. duinclostis. 



1. P. CAPITATUS Lamarck, 1813, p. 299 ; Harvey, 1858, p. 45, 

 PL XLIII.B ; P. B.-A., Nos. 271, 1475. Stipe up to 10 cm. high, 

 slender, not over 5 mm. diam., smooth, cylindrical, having at 

 the summit a subspherical head composed of slender, dichoto- 

 mous filaments, usually 100-200 ^ diam., with slight and dis- 

 tant constrictions, much calcified ; stipe extending to the center 

 of the head. Common in shallow water. Fig. 149. Fla., 

 W. I. 



2. P. DUMETOSUS (Lamour.) Decaisne, 1842, p. 97 ; Har- 

 vey, 1858, p. 44, PL XLIH.A; P. B.-A., No. 769. Stipe to 8 

 cm. high, 12-25 mm - diam., cylindrical or compressed, surface 

 uneven and granular ; at the summit a mass of dichotomous fil- 

 aments about as long as the stipe, 500-800 ^ diam., cylindrical 

 or compressed, somewhat calcified, distinctly constricted at 

 rather distant intervals. Fla., W. I. 



A stouter species than P. capitatus, with shorter and rougher 

 stipe, and larger head with larger and usually less calcified fila- 

 ments. It is rather common in our warmer waters, but not as 

 common as P. capitatus. 



3. P. LAMOUROUXII Decaisne, 1842, p. 97. Stipe 3-4 cm. 

 long, 6-8 mm. diam., smooth, rather soft and compressible, not 

 penetrating the head; head globose, 3-4 cm. diam., filaments 

 not abundant for the genus, 400-500 p. diam., ascending, 

 strongly calcified. Bahama, Jamaica. 



