7i’' -I
2. P entasterias margaritacea E h i.
P late L X X X V . F ig 7.
Char. Frond rough. Segments in front vieiv subglobose, attenuated
at their junction, icith short lateral converging
processes which are entire at their apices. End view with
Jive, rarelg six or seven, short obtuse rays.
Staurastrum margaritaceum Mcnegli., Synops. Desmid.
p. 227. ; Ralfs, in Annals, vol. xv. p. 157. pi. xi. fig. 7.
Eentastei'ias margaritacea Elir., Infus. p. 144. t. 10.
fig. 15.; Jenner, in loc. cit. p. 194.
Hah. Dolgelly : Mr. Ralfs. Ashdown Forest, Sussex:
3Ir. Jenner.
The rays arc much stouter and shorter in this than in the
preceding species.
3. P entasterias J enneri Hass.
Plate L X X X V . Fig. 6.
Char. Fronds large, dentated. Segments about as broad as
long, lengthened into a toothed angle on each side. End
view ivithfive, sometimes six, broad short-toothed rays.
Staurastrum Jennei'i Ralfs, in Annals, vol. xv. p. 158.
pi. xi. % . 8. ; Jenner, in loc. cit.
Hah. Mayfield, Sussex : Mr. Jenner.
A very fine species. “ The transverse view has a large
central opening surrounded by a row of large granules.” —
Ralfs. ^
55. A R TH R O D E SM U S Ehr.
Char. Fronds smooth, deeply constricted. End view compressed,
angles prolonged into a spine.
Derivation. From apdpov, a joint, and Ssagos, a linh.
The stout spines terminating the angles of the segments
seem to connect this genus with Xanthidium.
1. A rtiirodesmus convergens Ehr.
Plate L X X X V . Fig. 9.
Char. Segments broader than long, somewhat elliptic, elongated
at each side into an incurved spine. End viei\
compressed, with a spine at each extremity.
Artiirodesmus convergens Ehr., Infus. p. 152. t. 10. fig. 18.
Staurastrum convergens Menegh., Synops. Desmid
p. 228.; Ralfs, in Annals, vol. xv. p. 158. pi. xii. fig. 1.;
Bailey, Amer. Bacil. pi. 1. fig. 11.; Jenner, in loc. cit.
p. 194.
Hab. Brambletye, near East Grinstead; Rackham Common,
near Pulborough, Sussex; and Rusthall Common,
near Tunbridge W e lls ; Mr. Jenner. Dolgelly and
Penzance : Mr. Ralfs. Che sh u n t: A. H. H.
The incurved mucrones will at once serve to distinguish
this species.
2. A rtiirodesmus Incus Hass.
Plate L X X X V . Fig. 10.
Char, Segments externally lunate, ivitli a mucro at each
angle. End view elliptic, mucronated at each extremity.
Euastrum Bailey, Amer. Bacil. pi. i. fig. 12. ? Stam-astrum
Incus Meneghini, Synops. Desmid. p. 228.; Ralfs, in
Annals, vol. xv. p. 159. pi. xii. fig. 2.; Jenner, p. 194.
Hab. Weston Bogs, near Southampton; Rackham Common,
near Pulborough, Sussex ; Mr. Jenner. Dolgelly
and Penzance : Mr. Ralfs.
The mucro in this species is turned outwards : in the front
view the segments resemble those of Trigonocystis mucro-
nata, b u t the end view is very different.
3. A rtiirodesmus octocornis Ehr.
Plate L X X X V . Fig. 11.
Char. Fronds compressed. Segments broader than long,
A A 3