ARCHER, ON A NEW SPECIES OP ANKISTRODESMUS. 257 



a character, us I apprehend, of primary importance in sepa- 

 rating Closterium from Ankistrodesmus. Conceii-ing that I 

 am right in supposing my plant to be specifically identical 

 Tvith theirs, and as I think my account of the cell-division to 

 be correct, I believe I am justified in referring the plant in 

 question to Ankistrodesmus, and not to Closterium. To 

 adopt the plan I have pursued in regard to species, let us 

 compare and contrast for a moment the genera Closterium and 

 Ankistrodesmus ; the latter genus, I think there can be no 

 doubt, is quite equivalent to Raphidium, Kg., and I cannot 

 see why Kiitzing should reject a prior name. 



Closterium and Ankistrodesmus agree, then, in the cells hav- 

 ing an elongate, more or less attenuated, often arcuate, form ; 

 but they differ in several striking points. In the former genus 

 there is always a pale transverse band at the middle of the 

 frond or cell, and arising from a suspension or interruption 

 of the denser endochrome at this region ; and this pale space 

 is apparent, no matter what side of the frond is towards 

 the observer. In the latter genus there is, indeed, often a 

 clear space at the middle (as indicated in the form under 

 consideration), but it seems to me of a difi'erent nature. 

 Here, in fresh specimens, it does not form a transverse band, 

 due to interruption of endochrome, but a rounded or semi- 

 circular or oblique, smoothly defined spot (of nuclear import?), 

 laterally disposed, and closely approximated to the boundary 

 wall, that is, eccentric and parietal. It is true that it some- 

 times looks as if it were not so; but I am disposed to think 

 that this appearance is only when it is uppermost, and con- 

 sequently towards the observer ; while, on the other hand, as 

 is frequently the case, it may appear absent when it is on the 

 side turned away from the observer. In Closterium it is true 

 that a rounded body occupies the middle of the clear space 

 (possibly nuclear); but it is, at all events, not parietal, but 

 placed in the very centre of the contents, and it looks, indeed, 

 scarcely different in nature from the scattered or longitudinal 

 series of amylaceous large granules frequently present, of 

 which it seems but to form one. Again, in Closterium there 

 is always a clear space at each extremity of the endochrome, 

 in which a greater or less number of opaque, very minute, 

 but sometimes variably sized, granules exert a remarkaljle 

 constant active movement (as is well known), which appa- 

 rently is maintained during the whole life of the organism. 

 In some species there appears a special vacuole in which tliese 

 occur, in others they merely occupy a vacant space imme- 

 diately beyond the rest of the endochrome, leaving the rest of 

 the frond clear. In Ankistrodesmus there are no such gra- 



