COSMARIUM. 21 



and Tomachar in Cromar, Aberdeen ; near source of 

 the Barvie, Kincardine (Roy $' Bisxett). Ben Lawers, 

 Perth ! Argyll ! 



IRELAND.- -Dublin and "Wicklow ( Archer). 



Gvoyr. Distribution.- -France. Germany. Galicia 

 in Austria. Norway. Sweden. Bornliohn. Finland. 

 Poland. JST. Russia. India. Ceylon (var.). Sumatra. 

 Samoa (var.). Central Africa. United States. 



C. Quadrum is the rarest of the C. con sper sum- group in the 

 British Islands, although one of the most frequent tropical 

 species. It is distinguished from all forms of C. conspersum 

 Miid C. marqaritatum bv the rectangular semicells with a 



U */ Q 



broad flattened apex which is slightly retuse 111 the middle. 

 The vertical view is also oblong with parallel sides, and the 

 granules are invariably reduced in size in the median portion 

 of the apex of each semicell. The cell-wall between the 

 granules is quite smooth. 



The smaller forms of this species are known as : 



Var. MINDS Nordst. Norges Desm. 1873, p. 11; IJe Toni, 



Syll. Alg. 1889, p. 985; Schmidle, Beitr. Algenfl. Schwarz- 



wald. u. Kheiiieb. 1893, p. 101; Borg. Ferskv. Alg. Ostrgronl. 



1894, p. 14; etc. Length 38-50^; breadth 38-48 /* ; thick- 



ness 18 23ju. 



C. Pseudobroomei Wolle var. madagascariense W. & G. S. 

 West, Alg. Madag. 1895, p. 03, t. 7, f. 34 is very near to 

 C. Quadrum var. minus. It differs from the latter, however, 

 in its convex apices and in the reduction of the granules near 

 the centre of the semicells. It might best be regarded as a 

 form of C. Quadruin, under the name " C. QUADRUM var. 



3IADAGASCARIEXSR nob." 



Two other Desmids require mentioning in reference to 

 C. Quadrum. The first one is C. sublatum Nordst. (' Fresh w. 

 Alg. X. Zeal. & Austral/ 1888, p. 45, t. 5, f. 1-4). We give 

 a figure of a specimen from Australia (Victoria) for compari- 

 son with the figures of 0. Qaadrum. It differs only in two 

 points, in the hollow granules and in the inter granular punc- 

 t illations. These are scarcely specific differences, as even a 

 form of C. mar gar it at um is known with hollow granules. It 

 would be better placed as C. QUADRUM var. SUBLATUM (PI. C. 



The second one is C. Pardalis Colin, which is more especially 

 a tropical species. It is more angular than C. Quadrum, 

 with larger granules and intergranular punctulations. It is 



