78 BRITISH DESMIDIACEJE. 



/3. Lateral lobes with, fewer divisions ; interlobular in- 

 cisions widely open. 



15. M. radiata. 



16. M. Crux-Melitensis. 



SECTION C. Polar lobe with accessory processes ; lateral lobes of 

 semicells two, symmetrical or asymmetrical. 



17. M. Americana. 



18. M. Mahdbuleshwarensis. 



1. Micrasterias oscitans Ralfs. 

 (PL XLI, figs. 1-4.) 



Micrasterias ? oscitans Ealfs in Jemier's Flora Tunbridge Wells, 1845, 

 p. 198 ; Ralfs, Brit. Desm. 1848, p. 76, t. 10, f . 2 ; Eabenh. Flor. Europ. 

 Alg. Ill, 1868, p. 189; Wille, Gorges Ferskv. Alg. 1880, p. 21, t. 1, 

 f. 4, 5 (fonnae) ; Wolle, Desm. U.S. 1884, p. 116, t. 33, f. 3, 4; De Toni, 

 Syll. Alg. 1889, p. 1110; Eoy & Biss. Scott. Desm. 1893, p. 174. 



Holocystis oscitans, Hass. Brit. Freslrw. Alg. 1845, p. 387, t. 90, f . 4 ; 

 Bennett, Freshw. Alg. Eng. Lake Distr. 1886, p. 7, t. 1, f. 7-10. 



Euastrum (Micrasterias) oscitans Nag. Gatt. einz. Alg. 1849, p. 123. 



Tetrachastrum oscitans, Dixon in Proc. Dnbl. Nat. Hist. Soc. 1859 ; p. 205 ; 

 also in Quart. Jonrii. Micr. Sci. 1859, p. 83. 



Helierella oscitans Kuntze, Kev. gen. plant. 1891, p. 899. 



M. oscitans a typica Turn. Freshw. Alg. E. India, 1893, p. 88. 



Cells of medium size, about as long as broad, deeply 

 constricted, inner half of sinus usually narrowly linear, 

 outer half open and acutely conical ; semicells three- 

 lobed ; polar lobe wide, fusiform or subfusiform, with 

 acuminate (rarely bifid) poles and a convex apex ; 

 incisions below the polar lobe deep and somewhat 

 widely open ; lateral lobes horizontal, ovate-triangular, 

 with minutely bifid extremities. Side view of semi- 

 cell elliptic-pyramidate, with a rounded apex. Vertical 

 view elliptic-fusiform, with acuminate (very rarely 

 bifid) poles. Cell-wall minutely punctate. 



Zygospore unknown. 



Length 125-146 ^ ; breadth 123-135 /*; breadth of 

 polar lobe 91-95 p; breadth below polar lobe 52-56 p\ 

 breadth of isthmus 24-26 JJL ; thickness 44-52 p.. 



ENGLAND.- -Kirk Fell, Cumberland ! Westmoreland 

 (Ralfs). Sussex (Ralfs). Chobham Common, Surrey ! 



WALES.- -Capel Curig (Oooke $* Wills) and Moel 

 Siabod !, Carnarvonshire. Dolgelly, Merioneth (Rolfs). 



