72 BRITISH DESMIDIF.^E. 



4. M. radiosa (Ag.) ; frond orbicular, smooth ; segments five-lobed ; 

 lobes dichotomously divided ; ultimate subdivisions inflated, atte- 

 nuated at the end. 



Micrasterias radiosa, Ag. Bot. Zeit. 182/. 



Euastrnm Sol, Ehr. Verbreitung imd Einfvss des mikroskopischen Lebens 

 in Sad- iind Nord-Amerika, 1843, t. 4. f. 16. 



In a small pool a little below the ovitlet of Llvn Gwernan near Dolgellev, 

 J.R. 



jMaine to Virginia, Bailey. 



The frond, which is about the size of that of M. rotata, is orbicular ; seg- 

 ments five-lobed. The end lobe is narrow-cmieate, emarginate, and its angles 

 dentate. Tlie lateral lobes are dichotomously di\'ided as in all the preceding 

 species, but the subdi^dsions, especially the ultimate ones, are somewhat inflated, 

 and their extremities are either bidentate or taper into a short mucro. 



Micrastei'ias radiosa approaches M. rotata more nearly than any other 

 species, but it differs from all in its inflated subdivisions. The extremities of 

 the subdivisions m all the preceding species are truncate, but in this they 

 usually taper into a point. 



Length of frond y^^ of an inch ; breadth yig . 



Tab. VIII. fig. 3. a. frond with endochrome ; b. empty frond. 



5. M. jmpUlifera (Breb.) ; frond orbicular, with marginal gland-like 

 teeth ; segments five-lobed ; lobes dichotomously incised ; the prin- 

 cipal sinuses bordered by a row of minute granules. 



Micrasterias 2)apiUif era, Brebisson in lit. cum icone (1846). 



Hab. Dolgelley and Penzance, /. R. Sussex, Hants and Surrey, Mr. Jenner. 

 Ambleside, Mr. Sidebotham. Aberdeen, Br. Dickie and Mr. P. Grant. 



Falaise, Br/'bisson. West Point, New York, Bailey. 



The frond is smaller than in 31. rotata ; the segments five-lobed ; the end 

 lobe is nearly as broad as the others and emarginate, its angles are dentate. 

 The lateral lobes are usually equal and dichotomously divided, the incisions 

 rather shallow, and the ultimate subdivisions terminated by two or three gland- 

 like teeth. 



The surface of the frond has a row of minute hyaline granules or spines 

 bordering the iirincipal sinuses, but in other respects it is smooth. Except in 

 the empty frond, these granules, though sometimes evident, are frequently de- 

 tected with difficulty ; in order to perceive them, the lens should be gradually 

 withdrawn until the endochrome becomes less distinct, when they will appear 

 like puncta. 



The endochrome is brownish green, and the starch vesicles minute and 

 numerous. 



The sporangia, which I have gathered at Dolgelley, are similar to those of 

 M. denf/rii/afa, but smaller. 



M. papiUifera is a very distinct species, and its characters were detected 



