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



i. HALICYSTIS Areschoug, 1850, p. 447. 

 Frond unicellular, multinucleate, saccate, with narrow basal 

 portion; chromatophores minute disks without pyrenoid. 

 Asexual reproduction by biciliate zoospores without stigma, es- 

 caping through one or more openings ; similar but smaller 

 zoogarnetes (?) formed in separate individuals ; after the emis- 

 sion of the spores the openings close and several new genera- 

 tions of spores can be similarly produced. 



Though this genus was proposed for the following species as 

 long ago as 1850, its validity has been questioned, but studies 

 by Kuckuck, 1907, remove all doubt. 



H. OVALIS (L/yng.) Areschoug, 1850, p. 447 ; Kuckuck, 1907, 

 p. 139, PI. III. Fronds solitary or gregarious, obovate-ovoid, 

 y^-i cm. high, about half as wide ; membrane tough, 10-12 /u. 

 thick ; basal prolongation penetrating the substratum ; zoo- 

 spores 12-14X7-8 /u. ; gametes (?) 7-8X2-3 /x. Fig. 130. Van- 

 couver Island to Monterey, Cal. Northern Europe. 



This species has always been found growing on crusts of 

 Lithothamnion or similar calcareous algae, the radical portion 

 boring deeply into the substratum, apparently like Gomontia. 



2. VALONIA Ginnani, 1757, p. 38. 



Fronds not calcified, at first a single ovoid or clavate multi- 

 nucleate cell, producing more or less numerous cells similar in 

 form to itself ; this process being repeated more or less fre- 

 quently in different species; unicellular rhizoids being similarly 

 produced ; chromatophore forming a network with many pyre- 

 noids ; asexual reproduction by 2- or 4-ciliate zoospores, escap- 

 ing through numerous openings, and developing at once into 

 plants similar to the parent. 



As long as V. ovalis was included in this genus, it was diffi- 

 cult to define the latter clearly ; by the removal of that species 

 as Halicystis ova/is, the matter is much simplified. 



KEY TO THE SPECIES OF 

 i. Frond bullate, unbrauched. i. V. I'entricosa. 



i. Frond more or less abundantly branched. 2. 



2. Cells obovate-clavate, sparingly and irregularly branched. 



2. V. utricnlaris. 



2. Cells subcyliudrical. 3. 



3. Branches irregularly placed. 3. V. aegagropila. 



3. Branches in regular whorls. 4. 



4. Whorls frequent and dense; cells rather short. 



4. V. verticillata. 

 4. Whorls distant and loose, cells long. 5. V. confervoides. 



