THE YAN YEAN RESERVOIR, VICTORIA. 61 
Hab. Yan Yean Reservoir, at the weedy margin (June 1905). 
This deeply constricted Cosmarium appears to be referable to C. tjibenon- 
gense, Gutw., but the specimens possessed more regular semicells than would 
be inferred from Gutwinski’s figure. It seems most closely allied to C. con- 
tractum, Kirchn., differing in the hexagonal form of the semicells and in its 
lobed chloroplasts. 
24. COSMARIUM PERFISSUM, sp. п. (РІ. 4. fig. 2.) 
C. parvum, circiter 11-plo latius quam longum, profundissime constrictum, 
sinu aperto (ad apieem angusto sed extrorsum gradatim ampliato); semi- 
cellule anguste oblongo-ellipticæ, ventre leviter convexiore quam dorso, in 
medio apicis сит undulis minutissimis binis ; a vertice visæ anguste oblongo- 
ellipticæ, ad medium utrobique leviter inflatis ; a latere visæ subcirculares ; 
membrana subtiliter scrobiculato-punctata ; pyrenoidibus singulis. 
Long. 23-24 ш ; lat. 30-31 р; lat. isthm. 4 р; crass. 15 р. 
Hab. Yan Yean Reservoir, in the plankton (Mar.-May 1905) and at the 
weedy margins (Mar.-July and Dec. 1905). 
This species is а near relative of C. depressum, (Nüg.) Lund., but as it 
possesses very constant characters which readily distinguish it and render it 
easy of recognition at all times, it is perhaps best to regard it as specifically 
distinct. А form of C. Phaseolus occurred amongst it, but the two Desmids 
were obviously not the same. С. perfissum is distinguished from C. depressum 
by its deeper constriction, its very narrow isthmus, the more open sinus, the 
presence of the two minute undulations in the middle of each apex, and by 
the slight inflation on each side of the vertical view. The cell-wall is also 
more distantly punctated, and the punctulations themselves are larger. 
25. CosMARIUM PHASEOLUS, Bréb. in Menegh. * Synops. Desm.y Linnea 
(1840), p. 220; W. & G.S. West, Brit. Desm. ii. (1905) p. 158, t. 60. 
figs. 12-14. 
Forma semicellulis depressis, tumore centrali reducto et minute punctulato. 
Long. 28-30 ш; lat. 28-30; lat. isthm. Ty; crass. 14:5 ш. (РІ. 4. 
fig. 1.) 
Hab. Yan Yean Reservoir, at the weedy margins (Mar., Apr., June, July, 
and Dec. 1905 ; Jan. 1906). 
26. COSMARIUM ACHONDROIDES, sp. п. (Pl. 4. figs. 9-10.) 
C. mediocre, circiter tam longum quam latum, profundissime constrictum, 
sinu ad apicem angusto sed extrorsum valde aperto ; semicellulæ subhexagono- 
ellipticæ, dorso convexiore quam ventre, angulis lateralibus subrotundatis, 
apice in medio subrecto vel levissime retuso ; a vertice vise ellipticæ; a 
