32 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



without any definite radial arrangement, erect portion composed 

 of sliort, fairly definite, unbranched filaments with cells 2.8-3.2 n 

 diam., and aljout the same in length ; gonidangia all terminal and 

 simi)le, 4.5-6 .u diam. ; gonidia 1-1.5 n diam. 



Growing on CladopJiora sj). in a pool about four kilometers 

 north of Mayagiiez. The only sijecimen of the species is no. 

 1323 h, type. 



This is the smallest species of the genus that has been pub- 

 lished. It has a very definite and characteristic method of de- 

 veloping the basal portion of the thallus. The gonidium divides 

 into two cells, after which each elongates and divides in the plane 

 perpendicular to the first, producing four cells of equal size. 

 Any one or all of these four cells may divide, but usually the 

 plane of division is radial from the center of the four. After 

 this the dividing planes are usually in any direction perpendicu- 

 lar to the host, and the radial arrangement of the cells soon dis- 

 appears. Divisions of the cells in the center of the thallus by 

 planes horizontal to the host i^roduce the erect series of cells, 

 in this case unbranched and each series composed of three to 

 five cells. 



There is very little choice as to whether this species should be 

 placed in the genus Pleurocapsa or Radaisia. 



Radaisia Willei sp. nov. 



Thallus very variable in shape and size, 30-40 n thick ; early 

 stages in the development unknown ; erect filaments more or less 

 branched and coalesced, irregular in diam., composed of cells 

 3.5-5 n diam., one-half to one-third as long as the diam.; color 

 purplish violet ; gonidangia terminal, simple. 



Growing on stones in company with several other species of 

 Myxoijhyceae in a brook west of Humacao, no. 593, type. 



It is very difficult to make out the limits and character of 

 the basal portion of this species because of the presence of other 

 encrusting ]\[yxopliyceae, e.g., Xenococcus, with which it has to 

 compete for space. 



Radaisia confluens sp. nov. 



Thalli more or less indefinite and confluent, 50-60 m thick, 

 the early stages in the development unknown; erect filaments 

 more or less compound and branched, closely crowded and con- 



