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



generally simple, occasionally with a few rudimentary ramelli. 

 Guadeloupe. Australia. 



The ramuli in this species originate in the same way as in B. 

 plumosa, but instead of continuing the distichous arrangement, 

 both series bend towards the same side, until their direction is 

 the same, and the branching appears secund. B. Harveyana 

 has the same branching, b'ut the ramuli are stouter, and instead 

 of forming a definite plumule over all but the base of the rachis, 

 occur in short series, below the naked tip. This species is here 

 included from the reference in Agardh, 1886, p. 26, and the de- 

 scription there given is copied ; the original description by Son- 

 der is very meager ; it is not clear just how it is to be distin- 

 guished from forms of B. Harveyana. 



Family 3. DERBESIACEAE. 



Frond filiform, unicellular or with occasional partitions, mul- 

 tinucleate, simple or branched, with no differentiation of axis 

 and branches ; chromatophores numerous disks, with or with- 

 out pyrenoids ; asexual reproduction by large, multiciliate /oo- 

 spores, each with one nucleus, formed in lateral cells partitioned 

 off from the filaments. Only one genus. 



DERBESIA Solier, 1847, p. 158. 

 Characters of the family. Marine. 



KEY TO THE SPECIES OF DERBESIA. 



I. Filaments 100-600 /u. diarn. 3. D. Lamourouxii. 



i. Filaments less than 100 n diam. 2. 



2. Branching mainly dichotomous ; pedicel of sporangium about 15 M 



diam. i. D. vaucheriaefonnis. 



2. Branching mainly lateral ; pedicel 25-35 /x diam. 2. D. marina. 



i. D. VAUCHERIAEFORMIS (Harv.) J. G. Agardh, 1886, p. 

 34; P. B.-A., No. 318; D. tenuissima Farlow, 1881, p. 60, PI. 

 IV, fig. 4; Chlorodesmis vaucheriaefonnis Harvey, 1858, p. 30, 

 PL XL.D. Filaments erect, 40-50 //. diam., dichotomously 

 branched, up to 4-5 cm. high, in dense fastigiate tufts ; on one 

 or both branches, a short distance above the forking, two parti- 

 tions are often formed, the space between being 30-35 ^ in 

 length, and about the same diam. Sporangium formed in the 

 place of a branch, ovoid or broadly pyriform, i9o-3ooX 100-130 /x, 

 supported by a slender pedicel, about 15 ^ diam., 50-100 p. long, 

 in which two partitions, similar to those at the base of a branch, 

 enclose a cell 2-4 times as long as broad; spores large, about 15 

 in a sporangium. Southern Mass., Fla. 



