398 



[Vol. 10 



GARDEN 



Genus chondrocystis Lemm. 



Chondrocystis Schauinslandii Lemm. in Abh. Nat. Ver. Brem. 



16 J : 353. 1899. 



Associated with Ritwlaria coadunaia encrusting a sunken board; 

 only previously known from the Island of Laysan, Hawaiian 

 group, Pacific. 



Cut-off Pond, south end of Stump Lake. 



PI. 21, fig. 2 



Genus rhabdoderma Schmidle & Lauterborn 



Rhabdoderma sigmoidea sp. nov. PI. 21, fig. 1. 



Cellulis minutis, diametro circiter V/y-h- (plerumque 3-) plo 

 longioribus; reniformibus, curvatis vel sigmoideis, rarissime 

 ellipsoideis ; apicibus rotundatis; solitariis, in familias haud 

 consociatis; libere natantibus; contentu aerugineo homogeneo. 



Long. 4-13 n; crass. 2-3 n. 



Hab. In flora pelagica lacus, North Dakota. 



Mission Bay; Mission Lake; East Lake. 



Forma minor 



Cellulis minoribus et paullo gracillioribus. 



Long. 5-10 \l; crass. 1.5 p. 



Lake P. 



This minute alga occurred in great quantity and formed the 

 principal constituent of the collections taken from the above- 

 mentioned lakes. No trace of a gelatinous secretion leading to 

 the formation of definite colonies could be detected, but it is 

 possible that the long preservation to which the samples had been 

 subjected (1-3 years in dilute formalin) might result in the 

 disintegration of colonies of a delicate nature. The cells seemed 

 to be floating quite independently of each other, only occurring 

 rarely in short chains of two cells together, owing to slow separa- 

 tion after cell division. This new form differs markedly from 

 Rh. lineare, the only other species of the genus, not only in its 

 proportionate shorter and stouter cells, but also in its more 

 distinctly curved and often sigmoid form. The forma minor is 

 somewhat similar to the earlier described species but it is smaller 

 and has the typical curved or sigmoid form of Rh. sigmoidea. 



