Mr. J. Ralfs on the Nostochinez. 337 
a definite gelatinous sheath; ordinary cells subspherical, com- 
pressed, about as long as wide; vesicular cells subspherical, some- 
what barrel-shaped, half as wide again as the ordinary cells, puncta 
very distinct ; sporangia cylindrical, very unequal in length, and 
with the ends rounded and somewhat truncated. 
Occurring amongst other algz from a freshwater boggy pool at 
Wareham, Dorsetshire, Rev. W. Smith. 
D. Smithii is immediately distinguishable from its congeners 
on account of its possessing a definite gelatinous sheath to 
each of its filaments, which are of smaller diameter than those 
of any other species of Dolichospermum we are now describing. 
The ordinary cells are subspherical, somewhat compressed, and 
of less diameter than the vesicular cells, which are barrel-shaped 
and with very distinct puncta. The numerous sporangia, which 
are of about twice the diameter of the ordinary cells, are elon- 
gated and cylindrical, very variable in length and in the number 
which occur together, and their ends are slightly truncate. 
PuLaTE IX. fig. 4. 
5. D. Thwaitesii ( ). Filaments straight or nearly so; ordinary 
cells quadrate ; vesicular cells oblong, subquadrate, puncta very di- 
stinct ; sporangia numerous, cylindrical, with truncated ends, very 
variable in length. Spherozyga Ralfsii, Thwaites in lit. (1849). 
Ina freshwater pool, Dendham Down near Bristol ; also in a brack- 
ish ditch near Shirehampton, G. H. K. Thwaites. 
D. Thwaitesii is nearly allied to the foregoing species, but its 
filaments are not included in a definite gelatinous sheath. Its 
filaments are also stouter than those of D. Smithii, and there is 
a difference in the form of its ordinary as well as of its vesicular 
cells. The vesicular cells of D. Thwaittesii are quadrangular, and 
hardly exceed in diameter the ordinary cells. The cylindrical 
truncated sporangia are numerous, occurring many in a chain, 
and very variable in theiy length; they are of about twice the 
diameter of the ordinary cells. 
PuaTE IX. fig. 5. 
CyLinpRosPeRMuM, Kiitzing. 
Filaments simple, jointed, nidulating in a gelatinous stratum ; 
vesicular cells terminal ; sporangia oblong or elliptic, inter- 
posed between the vesicular and ordinary cells. 
(Anabaina, Bory and others.) 
In Cylindrospermum the stratum is similar to that described 
under the preceding genera; but as the filaments radiate less 
than is usually the case in Spherozyga, I was, in one instance of 
admixture, enabled to separate the Spherozyga from the Cylin- 
Ann. & Mag. N. Hist. Ser.2. Vol. v. 22 
