SPERMOSEIRA. 033 



most distant from the ciliated connecting one." Thw. Harv 

 Phyc. Brit, t, cxiii. B. 



On the muddy sides of ditches of brackish water, also floating. Dolgelly 

 Mr. Ralfs. Shirehampton, Mr. Thwaites. Portbury, Somerset, Mr 

 Broome." Very gelatinous, deep green, sometimes almost black. ' Fila- 

 ments pale green, curved, entangled ; connecting-cells large, ciliated, sub- 

 spherical, slightly oblong, of a lighter colour than the ordinary cells, which 

 are somewhat compressed. Spores of a deep brown when mature." Thw. 



3. S. Broomei, Thw. ; " spores numerous, elliptical, twice 

 as long as wide, not much exceeding in width the ordinary 

 cells, commencing to be formed from the cells nearest the 

 connecting- cells ; connecting-cells smooth, rather longer 

 than wide." Thw. Harv. Phyc. Brit. t. clxxiii. A. 



Ditches at Shirehampton, Mr. C. E. Broome and Mr. Thwaites. " A 

 very distinct species, first detected by C. E. Broome, Esq., an excellent 

 cryptogamic botanist, after whom it is named." Thw. 



4. S. Berkeleyana, Thw. ; spores large, twice the width of 

 the ordinary cells, oblong, half as long again as wide, becom- 

 ing brown when mature, generally two on each side the con- 

 necting-cell, which is spherical, slightly compressed ; young 

 filaments included, one or several together, in a defined, mu- 

 cous sheath." Thw. Harv. Phyc. Brit. t. clxxiii. B. 



Ditches at Shirehampton, Mr. Thwaites. " This fine species, which is 

 named in honour of the Rev. M. .T. Berkeley, is interesting from the cir- 

 cumstance of its filaments, when young, being enclosed, often several 

 together, in definite, gelatinous sheaths, out of which they appear to es- 

 cape before the spores are mature. There are other species, occurring in 

 fresh-water, which exhibit the same peculiarity of structure, but it does not 

 seem to have hitherto been noticed." 



5. S. Ralfsii, Thw. MS. ; filaments straight or nearly so ; 

 ordinary cells sub-quadrate; spores cylindrical with trun- 

 cated ends, of very unequal length, and scattered irregularly 

 throughout the filament ; connecting-cells oblong. 



In brackish and in fresh-water ditches near Bristol, G. H. K. Thwaites. 

 For the reception of this and some other closely allied species it is proposed 

 to constitute a new genus (Dolichospermum), characterized by their spores 

 being of unequal length and scattered irregularly throughout the fila- 



III. SPEKMOSEIRA. Ag. [Plate 27, E.] 



" Filaments slightly mucous, free, simple, cylindrical, en- 

 closed in a very delicate, membranous tube. Cells lenticu- 

 lar ; connecting-cells larger, compressed." Thw. Spores 



