COSMABIUM. 209 



variable, as is likewise their disposition. The apex in these 

 forms is usually smooth, but sometimes it is quite as granulate 

 as in typical C. punctulatum. 



The forms with the differentiated central granules and the 

 smooth apex have mostly been relegated to C. subpunctulatum 

 Nordst., but a wide experience of all these forms has con- 

 vinced us that it is not advisable to completely separate 

 C. subpunctulatum from C. punctulatum. Many intermediate 

 states occur, and some of them are of such a nature that it 

 would be exceedingly difficult to decide with any degree of 

 certainty whether they should be regarded as C. punctulatum 

 or C. subpunctulatum. Under these circumstances we have 

 considered C. punctulatum more in the light of a " species- 

 g'roup/' with C. subpunctulatum as one of its extreme forms. 

 The forms embraced in this " species-group " are C. punctu- 

 latum and several described varieties, C. polonicum Racib. 

 and described varieties, C. granulusculum Roy & Biss., and 

 C. subpunctulatum ISTordst. Others are also closely related, 

 such as C. anisochondrum Nordst. and C. bipunctatum Borg., 

 and it is possible that when more is known concerning these 

 species they also will have to be placed in the same species- 

 group. 



Nordstedt has mentioned the occurrence of a trigonal form 

 of C. punctulatum (consult Norclst. ' Norges Desm/ 1873, 

 p. 14). The smallest forms are from West Africa: length 

 18 fj. breadth 18 /.t ; breadth of isthmus 6/z; thickness 9 /UL 

 (consult W. & Gr. S. West, ' Welw. Afric. Freshw. Alg.' 1897, 

 p. 121). 



Var. subpunctulatum (Xorclst.) Borg. 



Cosmarium subpunctulatum Nordst. in Botaii. Notis. 1887, p. 161 ; Freshw. 



Alg. N. Zeal. 1888, p. 47, t. 5, f. 8 ; De Toni, Syll. Alg. 1889, p. 1049 ; 



Borge, Bidr. Siber. Chlor. 1891, p. 11; West, Alg. W. Ireland, 1892, 



p. 154; Eoy & Biss. Scott. Desm. 1894, p. 175; Nordst. Index Desui. 



1896, p. 246 ; West & G. S. West, Alg. S. England, 1897, p. 488 ; Alga-fl. 



Torks. 1900, p. 76 ; Notes Alg. II, 1900, p. 293, t. 412, f. 9 ; Alg. N. 



Ireland, 1902, p. 38 ; Freshw. Alg. Orkneys and Shetlaiids, 1905, p. 20. 

 C. punctulatum Breb. var. subpunctulatum (Nordst.) Borg. Ferskv. Alg. 



Ostgronl. 1894, p. 11 ; Borge, Siisswasseralgen Siid-Patagon. 1901, p. 



21 [forma major], 



Semicells with well marked central granules often 

 situated on a very slight central inflation ; disposition 

 of central granules very variable, but commonly in a 



O / y 



somewhat irregular ring of 6-8 surrounding a central 

 one. 



VOL. III. 14 



