PLEUROCARPUS. 231 



MESOCAEPUS EECUEVUS, Hass. 



Diameter of filaments, 10-18 //; cells 5-10 times longer 

 than broad, more or less recurved. Zygospores globose, 

 membrane smooth, diameter, 20-24 yw. 



Syn. Sphaerocarpus recurv us, Hass. 



Ponds and ditches. 

 Plate CXLVII, fig. 6, conjugating filaments and spores. 



MESOCAEPUS EADICANS, Kg. 



Diameter of filaments, 22-29 ^ ; cells 3-8 times as long as 

 wide. A sterile form scarcely to be counted a distinct 

 species, possibly a variety, or condition of M. scalaris, pos- 

 sessing the singular feature of short branchlets usually 

 emitted nearly at right angles, about the middle of a cell. 



Plate CXLVIII, figs. 7-10, sterile, branched filaments. 



The arrangement of the endochrome and of the starch 

 grains in the cells, are a good illustration of sterile filaments 

 of nearly all species. 



Spore membrane punctate. 



MESOCABPUS NUMMULOIDES, Hass. 



Diameter of vegetative filaments, 9-15 /* ; cells 7-14 times 

 longer than broad. Spores spherical. 17-23 /* in diameter, 

 membrane punctate. 



Syn. Sphaerocarpus nummuloides, Hass. 



Meadow, or wayside pools. 

 Plate CXLVIII, figs. 1, 2, sterile and fruiting filaments. 



MESOCAEPUS EOBUSTUS, D. By. 



Diameter of filaments, 25-32 // ; cells 3-8 times longer than 

 broad, nearly straight ; spores nearly spherical, 40-50 yw 

 diameter, membrane reddish brown, finely punctate. 



Small ponds and ditches. 



Plate CXLVII, fig. 5, copulated cells, with spores too 

 nearly spherical for the typical form. 



Genus 76, PLEUEOCAEPUS, A. Br. 



Filamentous, cells the same as the cells of Mesocarpus; copu- 

 lation not scalariform, but lateral, by the flowing together of the 

 chlorophyl of two adjoining cells. Sterile filaments often bent 

 nearly at right angles, and united at the angles, but producing 

 no fruit. 



