DIMORPHOCOCCUS . 199 



back to back ; other specimens, probably only other stages 

 of development, are smaller ; again other families are com- 

 posed of larger and smaller forms intermixed ; some have 

 the ends more incurved than others. They occur in families 

 of two or four, and again in more or less spherical masses, 

 containing hundreds. The distinctions between the differ- 

 ent forms are not sufficiently constant to admit of separation. 

 Some of the larger forms agree well with Selenastrum Bibrai- 

 anum, Eeinsch, ends rather more acute ; the smaller forms 

 are _R. convolutum, var. lunare, Kirch., but evidently these 

 with numerous intermediate stages belong to the same 

 species. Length of larger cells, three to four diameters, 

 smaller ones about two diameters. 



Plate CLX, figs. 1, 2, 3, a larger form corresponding with 

 Selenastrum, Eeinsch ; figs. 4, 5, smaller form, often clustered 

 in large numbers ; figs. 28, 29, from a mass of hundreds of 

 the small cells and a comparatively few larger ones among 

 them. The larger, three times the length and breadth of 

 the smaller ones of the group. 



Genus 63, DIMOEPHOCOCCUS, A. Br. 



Cells united more or less in fours on short branches, the two 

 intermediate contiguous cells oblique, obtuse ovate ; the two 

 lateral, opposite and separate from each other, lunate ; families 

 free swimming, in botryoid clusters. A. Br. 



DIMORPHOCOCCUS CORDATUS, Wolle. 



Cells cordate, extrorsal reniform, obtusely ovate or oblong 

 curved with ends rounded, and sometimes with a deep notch 

 on one side ; singly, or united in rather irregular clusters of 

 2-4-8 cells conjoined ; sometimes forming coenobia, by 

 smaller families of cells connecting by slender, colorless, 

 radiating, gelatinous threads ; thread attached to the back 

 or rounded side of the cells. Diameter of cells, 4-8 ^ 

 usually twice as long as broad. Free swimming. 



Ponds, Pennsylvania, New Jersey, Florida. 



Plate CLX, figs. 30-35, coenobia in various stages of 

 growth ; figs. 36-38, simple group, as they often occur in 

 large numbers. 



Found the coenobia forms most abundant in small pools 

 in Florida. 



