20 COCCOPHVCE.E. 



Rhaphidium duplex. Xutz. Phyc. Germ. p. 144. 



Fusiform, slender, slightly sigmoid, single, or 2, 3, or 4 

 Laterally connected at the poles, otherwise free. 



Rhaphidium triplex, Rabh. Krypt. Fl. Sax., p. 134. 



Scenedesmus duplex, Ralfs Desrn. 193, t. 34, f. 17. 



Rhaphidium polymorphum var. d. sigmoideum, Rabh. Alg. iii. 

 p. 45. 



In pools (apparently rare). 



" Cells linear-lanceolate ; extremities tapering to a fine point and 

 curved in opposite directions. The cells closely united, frequently the 

 frond, consists of only a single pair of cells so connected, but sometimes 

 of two or even three of these pairs, which, however, are remote from 

 each other, in this case ; as the connecting macoua is colourless, they 

 look like distinct plants, and their relation can be detected only by 

 moving the frond. If kept in water fo^ a few days, the cells separate 

 from each other.' Ralfs. 



This description is scarcely accurate, as each cell is a distinct plant. 



Plate VIII. fig. 5. a, cells magnified 400 ; b, magnified 800 diam. 



GENUS 14. DICTYOSPHJERIU1YI. Nag. (1849.) 

 Cells elliptic, with thick confluent mucous investment, com- 

 bined in numbers into free-swimming one-layered hollow- 

 globular families, one always at the ends of delicate threads 

 which proceed from the central point of the family, and which 

 become repeatedly branched towards the periphery ; division at 

 the commencement of a series of generations in all directions of 

 space ; afterwards, as regards the middle point of the aggre- 

 gate family, as a rule, alternating only in the two tangental 

 directions. 



Only three described apecies, all of which have occurred in the British 



Isles. 



Dictyospheerium Ehrenbergianum. Nag. Einz. Alg. p. 73. 



Families aggregated in a globular, or broadly elliptical 

 figure ; cells elliptic, very minute, about one-third as broad as 

 long. 



SIZE. Cells -004--0075 mm. (Rabh.}, -004--007 mm. (Kirch.). 



Rabh. Alg. iii. 47. Kirch. Alg. Schl. p. 106. 



Amongst Confervoe. 



" This form is very minute, and in suitable places, common, the 

 families in the aggregate forming a globular, or broadly elliptic, or 

 sometimes subcubical figure ; the rate of growth of the delicate thread 

 being equal all round, the cells at the ends of each of its dichotomous 

 ramifications stand at nearly equal distance from the original centre ; 

 hence the regular figure of the aggregate family. The individual cells 

 are elliptic, and very minute." Archer. 



Plate IX. Jig. 1. Families magnified 400 diam. ; b, fragment with 

 cells X 400 dium. ; c, variety with spherical cells. 



ft 



