122 BRITISH DESM1DIACE.E. 



cesses. Vertical view rhomboid-fusiform, poles attenu- 

 ated and tridenticulate, at the middle on each side with 

 a small granulate or denticulate protuberance, polar 

 lobe showing very clearly the disposition of the four 

 processes. 



Zygospore unknown. 



Length 151-220 p.; breadth 185-1 90 ft; maximum 

 breadth of polar lobe 75-100 //, ; breadth of isthmus 

 19-22 p. ; thickness 40-47 ^ 



Geoyr. Distribution. Austria. Sweden. India. 

 Burmah. Siam. Java. New Zealand (var.). Aus- 

 tralia. E. Africa. Madagascar (var.). United States. 

 British Guiana. 



This species is principally tropical and subtropical in its 

 distribution, and the typical form has not so far been met 

 with in the British Islands. It is subject to great variation 

 in the length of the processes, both of the polar and lateral 

 lobes, in the amount of their divergence, and in the details of 

 the surface-markings. The lateral lobules are often sub- 

 divided, and the subdivision is exceedingly variable. This 

 has resulted in the naming of numerous varieties. 



Var. Wallichii (Grim.) nob. (PL LIV, figs. 7, 8; 



PL LV, figs. 1-3.) 



M. Wallichii Grun. Diat. u. Desm. Ins. Bank. 1865, p. 14, t. 2, f . 21 ; Arch, 



in Quart. Journ. Micr. Sci. 1865, p. 260, 261; Eabenh. Flor. Europ. 



Alg. Ill, 1868, p. 196 ; Lund. Desm. Suec. 1871, p. 15 ; Kirclin. Alg-. 



Schles. 1878, p. 161 ; De Toni, Syll. Alg. 1889, p. 1123 ; Turn. Freshw. 



Alg-. of E. India, 1893, p. 95: Nordst. Index Desm. 1896, p. 271. 

 M . Hermanniana Beinsch, Spfic. Gen. Alg. 1867, p. 120, t. 21 B, f . 1-4. 

 Didymidium (Micrasterias) Hermanniana Eeinsch, Algenfl. Frank. 1867, 



p. 141, t. 8, f. 1. 

 M. ampullacea Mask. N. Zeal. Desm. 1881, p. 304, t. 11, f. 6-8 [M. Mahdbu- 



leshwarensis (3 ampullacea Nordst 1888J. 

 M. Americana forma Wallichii Mask. Note Micr. Americana, 1888, p. 9, 



t. 1, f. 9. 

 M. Mahabuleshii-arensis Hobson A. genuina a. indica Nordst. Freshw. Alg. 



N. Zeal. 1888, p. 31 [also various other forms]. 

 Helierella Wallichii Kuntze, Eevis. gen. plant. 1891, p. 899. 

 Micrasterias Wallichii f. typica Turn. Freslrsv. Alg. E. India, 1893, p. 95. 



t. 6, f. 1. 



M. Wallichii f. major Turn. 1. c. 

 H. Wallichii var. Hermanniana (Eeinsch) Turn. 1. c. [various forms, 



including M. ampullacea Mask.]. 



This variety is distinguished by the subdivision of 

 the superior lateral lobules, each of which is divided by 



