Mr. J. Ralfs on the Nostochinese. 335 



DoLiCHOsPERMUM, T/iwaites MS. 



Filaments simple, generally moniliform, aggregated into a gela- 

 tinous stratum ; sporangia interstitial, elongated, separated 

 from the vesicular cells by the ordinary joints. 



Dolichospermum differs from Sphceruzyga only in the different 

 arrangement of its cells. In the latter genus the vesicular cells 

 connect the sporangia, whereas in the former they are situated 

 amongst the ordinary cells. 



The sporangia are much elongated and mostly cylindrical. 

 They are developed from the ordinary cells, which are more or 

 less remote from the vesicular ones. Mr. Thwaites finds that 

 their extremities are invariably truncated, and the endochrome 

 escapes in an undivided mass, a circumstance he has not noticed 

 in the other genera belonging to the Nostochinece. 



This genus is distinguished from Cylindrospermum by the in- 

 terstitial position of the sporangia and vesicular cells, and from 

 Trichormus and Spermosira by its elongated sporangia. 



1 . D. incequale ( ) . Filaments moniliform ; ordinary cells at first 



quadrate, finally orbicular; vesicular cells large, spherical; sporangia 

 linear, catenate. 



Boggy pools. Dolmelynlyn near Dolgelley, J. R. 



This plant forms extensive strata, composed of thick gelatinous 

 masses of a deep green colour. Filaments elongated, consisting 

 of from 100 to 200 cells, and, being stouter than in most species 

 belonging to this family, visible to the naked eye. Ordinary cells 

 distinct, quadrate in immature specimens, but at length nearly 

 spherical, appearing punctate on accoimt of the scattered gra- 

 nular matter which they contain. Vesicular cells spherical, 

 broader than the ordinary joints and occurring at short intervals. 

 Sporangia three or four times longer than broad, with truncate 

 ends, in chains of from two to five members. 



Dolichospermum incequale may be known from the following 

 species by its spherical vesicular cells and catenate sporangia. 



Plate IX. fig. 1. 



2. D. Ralfsii (Kiitzing). Filaments moniliform; ordinary joints 

 spherical ; vesicular cells elliptic ; sporangia elliptic or cylindrical, 

 one or two in each series. Cylindrospermum Ralfsii, Kiitzing, Bot. 

 Zeitg. (1847), p. 197 ; Species Algarum, p. 293; Tabulae Phyco- 

 logicse, t. 98. fig. 7. 



Bog and rivulet at Llyn Gwernan near Dolgelley, /. R. 



Dolichospermum Ralfsii occurs in extensive strata of a velvety 

 rich dark green colour, sometimes verging towards jeruginous 

 green. A portion placed in water threw out, in the course of one 



