W. B. TURNER : NOTES ON FRESHWATER ALG^E. 



35 



sinus linear; end lobes truncate, with a stout spine or rostrum at 

 outer angle — these lobes are slightly exserted ; frond punctate. 



Long. 272 /x=-oio7 in.; Lat. max. 224 /z= '00882 in.; Lat. lob. 

 pol. apic. (s. sp.) H2 fx - '0044 in.; Lat. isthmi 37 [x= -00146 in. 

 Name from irkarvs broad, irrepov wing. Near to M. triangularis Wolle 

 and M. depauperata Nordst. (Note the latter species is described in 

 the Desmids of the U.S. America by Mr. Wolle as M. Kitchelii.) 

 Habitat, U. S. A. 



Staurastrum quadri-spinatum nov. sp. Of medium size, much 

 longer than broad ; frond smooth, or lightly punctate ; each angle of 

 the segments bearing four stout divergent spines ; ends of segments 

 slightly concave ; sinus wide, expanding rapidly. 



Long. (s. sp.) 34 /x= '00134 in.; Lat. (s. sp.) 26 p= '00102 in.; 

 Lat. isthmi 8 [x = -0003 in. ; Long. spin. 10 [* = '0004 in. Hab., Trelleck 

 Common, Monmouth ; also United States. 



I have been tempted to add a figure of Docidium (Triploceras) 

 verticillatum Bailey, for the reason that from its publication 

 (Smithsonian Trans. 1850) till now I have never seen a valid icon of 

 this species. Hab., U. S. A. 



Long, (semi-cell) 340 ^ = '0134 in. ; Lat. max. 46 [l = *ooi8 in. ; 

 Lat. apic. (s. sp.) 76 /* = '00299 in. 



Finally, I would remark, with respect to the Desmids, that our 

 knowledge of them is but slight; not a single 'life-history' is perfectly 

 known of a tribe numbering about 900 species, or with varieties 1,200. 

 The altitude as affecting their presence has very rarely been noted, 

 though we are aware that Didymoprium (Bambusind), Desmidium, 

 Docidium, and Closterium prefer the low-lands. My own notion is 

 that, while certain species are found everywhere, at moderately low 

 levels, from the Pole to the Equator, being thoroughly cosmopolitan, 

 geological influences have a ' decided something ' to do with certain 

 local species ; and I have long held the opinion (as yet unshaken) 



(1) that most Desmids prefer the Igneous geological districts to others; 



(2) that some are but rarely found in districts newer than the Old Red 

 Sandstone, e.g., Staurastrum ophiura, S. cerastes, S. Brasilietise (?), 

 S.arctiscon, Micrasterias brachyptera, &c; (3) that few are found in 

 chalk districts, or on the greensand; and (4) that they are most abundant 

 {at least the commoner species) when the water wherein they live 

 contains a small quantity of dissolved iron, though they will not 

 endure so much of this metal as will the Diatoms (with their yellow 

 or brownish endochrome), the colour of which a somewhat large 

 percentage of iron seems to enhance, while an excess kills them ! 



Feb. 1886. 



