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



rarely larger ; loosely united into light green, gelatinous masses ; 

 wall sometimes rather thick, hyaline, more or less distinctly 

 lamellate. Mass. Europe. 



Forming soft, easily scattered gelatinous masses on sub- 

 merged objects. 



3. C. ENDOZOICUM Collins, P. B.-A., No. 1323. Cells 10-25 

 /A diam., spherical, thin-walled. In the mantle of the mussel, 

 Mytilus edulis, in tide pools. Me. 



C. natans Snow, 1903, p. 383, PI. Ill, fig. XI, is uncomfort- 

 ably near C. infusionum, none of the characters given in the 

 description being distinctive. 



2. TROCHISCIA Kiitzing, 1845, p. 129. 



Cells globose or subglobose, with several parietal chromato- 

 phores and one or more pyrenoids, with thick membrane, 

 having various spines, ridges, or other projections ; asexual 

 reproduction rarely by cell division, more commonly by aplano- 

 spores, formed many in a cell by repeated division, escaping by 

 dissolution of the mother cell wall, with membrane at first 

 smooth, later developing characters of the mother cell. 



Some of the species of Trochiscia are fresh water plankton 

 algae, some inhabit moist places, especially dripping rocks. 

 Care is sometimes needed to distinguish them from spores of 

 desmids, or from unicellular stages of other algae. The knowl- 

 edge of the American species is nearly all derived from the 

 observations of Reinsch, 1886, and a careful comparison of his 

 descriptions and figures is likely to leave one in a state of seri- 

 ous doubt as to the validity of some of the species ; there 

 are certainly three types ; respectively with warty projections, 

 spines, and wavy ridges ; it may be that three species, one of 

 each type, would include all our forms. 



KEY TO THE SPECIES OF TROCHISCIA. 

 i. Membrane beset with papillae, spines, or wart-like prominences. 



2. 

 i. Membrane beset with wavy ridges. 5. 



2. Projections warty and irregular. 3. 



2. Projections spine-like. 4. 



3. Projections rather distant, bluntish ; cells 18-23 M diam. 



i. T. granulata. 

 3. Projections densely set, acutish ; cells 14-17 M diam. 



2. T. aspera. 



4. Spines pyramidal, of unequal length. 3. T. hirta. 



