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



The description given is made by combining the record of 

 Setchell and Gardner with that of Yendo. The arrangement of 

 the cells on long, dichotomous stalks, together with the firm, 

 solid frond, seem to justify maintaining Collinsiella as a genus 

 distinct from Ecballocystis. The transformation of vegetative 

 into motile cells has not been observed in the genus, but is to 

 be expected, as in other respects the genus resembles Prasino- 

 cladus. 



Order PROTOCOCCALES. 



Vegetative cells motionless, solitary or in spherical or net-like 

 combinations, rarely filiform. Cells uni-, rarely multi-nucleate ; 

 chromatophore usually single, disk- or cup-shaped. 



KEY TO THE FAMILIES OK PROTOCOCCALES. 



i. Cells free or united in gelatinous colonies. 2. 



i. Cells united in regular, net- or disk-shaped colonies, not gelatinous. 



5. HYDRODICTYACEAE. 

 2. Cells inultinucleate, relatively large, irregularly branched. 



2. PROTOSIPHONACEAE. 



2. Cells uninucleate, of definite form. 3. 



3. Cells spherical, relatively large, with many disk-shaped chromato- 



phores. 3. HAI/XSPHAERACEAE. 



3. Cells of various forms, with single chromatophore. 4. 



4. Cells dividing vegetatively. 4. SCENEDESMACEAE. 



4. Vegetative cell-division rare and abnormal. 



i. PROTOCOCCACEAE. 

 Family i. PROTOCOCCACEAE. 



Unicellular, spherical or pyriform, rarely irregular; free or 

 attached ; asexual reproduction by zoospores or aplanospores ; 

 sexual reproduction by zoogametes in some instances ; normal 

 cell-division rare and exceptional. Marine or fresh water. 



The genus Protococcns formerly contained a heterogeneous 

 collection of unicellular plants, which have since been all trans- 

 ferred to widely separated genera, and the genus is now hardly 

 recognized by any good authority. The order and family which 

 derived their names from it still remain in good repute. P. 

 ovalis Hansgirg in Foslie, 1890, p. 159, PI. Ill, fig. I2 , was 

 founded on a form found in tide pools near high water mark in 

 Norway, and the same form has been found in a similar station 

 in Maine. It has ovoid or ellipsoid cells, 8-10X9-12 /A, with 

 thin wall and yellow-green contents, solitary or congregated in- 



