201 

 which was of Leitz manufacture also. And this Amocboid form de- 

 vclop into a form which was likc Tab. XV. lig. 5 b. in The Bri- 

 tish Desmidieae. 



Peshaps 1 bettcr gire the synonym of Cosmarimn hioculatum, A. B. 



« C. hioculatum (Brcb.); frond smoth, constriction producing a 

 gaping notch on each side ; segments subelliptic, entire ; sporangium 

 orbicular, spinous. 



Helerocarpella bioculaia, Brébisson, Alg. Fai. p. 56. t. 7 (i835). 



Cosmarium bioculatiim, Brébisson in liti, [cum icone) (1846). 



Probably common. « England, Falaise, France and the United 

 States ». 



« Frond very minute, about as long as broad, deeply constricted 

 at the middle. The segments, which are elliptic, are connpcted by a 

 more distinct isthmus than in the allied species, hence these is a 

 wider notch on each side. The endochrome is usually more in the 

 centre of each segment. The empty frond is not punctate. 



The sporangium is orbicular and minute and has conical spines. 



Cosmarium bioculatunì differs from C. Phaseolus, Bréb. in its 

 similar size and more elliptic segments, which are not in apposition. 



1 wish to say in Desmidieae « species » do not exist only forms 

 which are changeable by evolution the one into the other. 



There are one or two points which 1 wish to make plain in the 

 consideration of the Desmidieae. The first is the point of the opi- 

 nions advocated on the relations of these Algae. 



Ralfs says The British Desmidieae page 7, « 1 wright to state 

 however that the opin'i'ons advocated above do not agree with those 

 of M. De Brébisson, who has attained so high a reputation for his 

 intimate acquaintance with the freshwater Algae, and to whose kin- 

 dness I bave been so often during the progress of the present work. 

 He considers that there is an essential distinction in the mode of di- 

 vision between the Desmidieae and Nostochineae (including in the 

 latter the Palmelleae), and that from it indeed differential characters 

 are obtained which we can distinguish these nearly-allied groups. 

 Ile observes of Hormospora mutabilis Bréb. (*j. Ils sont le plus sou- 



{}) Annales des Sciences NaUirelles, Jan. 1844. 



13 



