NITBLLA GRACIUS. 119 



showing about 8-9 convolutions ; coronula 25-30 /x 

 high persistent. Oospore very broadly ellipsoidal 

 c. 250-300 p. long, 225-250 p, broad, 1 75-200 ^ thick, 

 light brown, showing about 6 rather prominent 

 ridges; outer membrane thin, flexible and translucent, 

 bright yellow-brown, very finely granulate. (PL V, 

 f. 2,) Antheridiiun c. 300 /x in diameter. 



HABITAT. Pools, ditches and lakes ; very rare. 



DISTRIBUTION. England : Cornwall, AY., ditch near 

 Perranzabuloe, and pool, Newlyn East (F. Rilstone, 

 1912) ; Sussex, AY., boggy pool, St. Leonard's Forest 

 (TF. Borrer, 4th Sept. 1809); Salop, small deep pool, 

 locality not revealed (IF. E. Beckwith, 1883). 



Ireland : Wicklow, Lough Luggala and Lough Dan 

 (R. M. Barrington and H. $ J. Groves, 1892). 



First record: 'English Botany,' 1810, when the 

 species was originally described and figured. 



Outside the British Isles N. gracilis is recorded 

 from Norway, Sweden, Finland, France, Belgium, 

 Germany, Switzerland, Austria, Hungary, Italy, and 

 Russia ; also from Africa, Asia, North and South 

 America, and (?) New Caledonia. 



Typically a slender, delicate, extremely graceful plant, of 

 rather small stature (15-20 cm.) with lax whorls. It is dis- 

 tinguishable from typical N. mucronata, to which it is most 

 nearly allied, by its more slender and flexuous habit with the 

 rays usually more frequently forked, by the frequent occur- 

 rence of three-celled ultimate rays in which character it forms 

 a link between Braun's two sections Diarthrodactylae and 

 Polyarthrodactylae (the latter group not being represented in 

 this country), and by the penultimate cell being less rounded at 

 the apex, and not much broader than the base of the ultimate 

 cell, so that the ultimate cell does not appear as a definite mucro. 



The form collected by Mr. F. Rilstone in Cornwall, from 

 which our figure is taken, is an extremely beautiful and grace- 

 ful one ; that from Co. Wicklow is much larger and stouter, 



growing- in big- dense tufts with the branchlets as much as 



. 



4-5 cm. long and equalling or exceeding the mternodes. 



Braun tersely summarizes the variation in the species as 

 follows: "Variat crassior (forma bugellensis Rabenh.) et 



