cs 
THE YAN YEAN RESERVOIR, VICTORIA. 09 
Genus COSMARIUM, Corda. 
19. COSMARIUM DORSITRUNCATUM, (JVordst.) nob.—C. Scenedesmus, Delp., 
var. dorsitruncatum, Nordst. in К. Se. Vet. Akad. Handl. xxii. no. 8 (1885), 
р. 59, t. 3. fig. 15. 
C. parvum, circiter 14-plo latius quam longum, profundissime constrictum, 
sinu angustissimo-lineari cum extremo leviter ampliato ; semicellulæ depresso- 
subsemicirculares, angulis basalibus obtusis, apice leviter depresso; a vertice 
vise anguste ellipticæ, polos versus leviter attenuatis ; a latere vise circu- 
lares; membrana subtilissima punetato-granulata; pyrenoidibus conspicuis 
binis. 
Long. 30-32 р; lat. 38-42 p ; lat. isthm. 12-14 р; crass. 15-18 p. (РІ. 4. 
fip. 4.) 
Hab. Yan Yean Reservoir, at the weedy margins (Feb—Apr., and also 
Oct. 1905). 
This Desmid was described and figured from New Zealand as © C. Scene- 
desmus В dorsitruncatum?? by Nordstedt, who was in doubt, however, con- 
cerning the nature of the chloroplasts. It has been recorded by Raciborski 
from the Centenial Park, Sydney (vide Rospraw. Wydz. matem.-przyr. Akad. 
Umiej. Krakow. xxii. (1892) p. 373), and that author states that the chloro- 
plasts contain one pyrenoid. In this statement it would appear that Raciborski 
is incorrect. The specimens from Victoria were in absolute agreement with 
Nordstedt’s published dimensions and with his figure, but in all cases every 
semicell possessed a partially subdivided axile chloroplast containing {wo 
conspicuous pyrenoids. 
The cell-wall is most minutely granulate, so that the margin is very 
slightly rough. These granules ате less evident in the centre of the semicells 
than near the margins. 
C. dorsitruncatum differs from C. depressum, (Nüg.) Lund. (= C. Scene- 
desmus, Delp.) in its narrow, closed sinus, in the semicircular-depressed form 
of the semicells, in the minute granulation of the cell-wall, and in the presence 
of two pyrenoids in the chloroplast. The poles of the vertical view are also 
more attenuated. 
From C. Pseudoscenedesmus, W. & С. S. West (in Trans. Linn. Soc. ser. 2, 
Bot. vi. (1902) p. 164, t. 20. fig. 34), it is distinguished by its relatively 
greater length, its less deep constriction, its thicker vertical view, and by the 
dense but exceedingly fine granulation of the cell-wall. 
Quite recently Gutwinski has described a plant from Java under the name 
of * C. dorsitruncatiforme” (vide Bull. Acad. Sci. Cracovie, Nov. 1902, 
p. 592, t. 38. fig. 35). This is, however, merely one of the common tropical 
forms (rather small) of typical С. obsoletum, (Hantzsch) Reinsch, and 15 
mentioned as occurring in Koh Chang in the Gulf of Siam in Botan. Tidsskr.. 
