THE YAN YEAN RESERVOIR, VICTORIA. 71 
Cellule plerumque torte; long. cum proe. 35-39 р; lat. eum proc. 39-44 ш: 
lat. isthm. 4:5 р; crass. 75-8 р. (Pl. 6. figs. 15-16.) 
Hab. Yan Yean Reservoir, at the weedy margins (July, Nov., and Dec. 
1905 ; Jan. 1906). 
This peculiar Staurastrum was particularly common in July. The speci- 
mens agreed very well with those originally described from Madagascar, but 
the cells in nearly all cases were twisted at the isthmus, and the processes 
were minutely tridenticulate. Bohlin has recorded this Staurastrum from 
the Azores (vide Bohlin, in Bih. till K. Sv. Vet. -Akad. Handl. Bd. 27, no. 4 
(1901) p. 55, fig. 13), but was greatly in error in regarding it as allied to 
S. gracillimum var. biradiatum, W. & G. 5. West. The Desmid which 
Bohlin mentions and figures under the name of 5. gracillimum var. biradiatum 
is typical S. tetracerim, Ralfs, and there is little question that ©. hibrachiatim 
var. cymatium has had а direct origin from S. fetracerum. Specimens in 
which one semicell agrees with S. fefracerum are occasionally observed 
(РІ. 6. fig. 15; also Bohlin, l e. fig. 15), and the dentieulation of the pro- 
cesses is the same. The marked twisting of the cells at the isthmus is also 
a character in common with S. tetracerum. 
50. STAURASTRUM ExCAvATUM, W. & G. S. West, in Trans. Linn. Soc. 
ser. 2, Bot. у. (1895) р. 78, t. 8. fig. 42. 
Forma isthmo cellularum breviore et sinu minore, processibus eum undulis 
numerosioribus ; cellulis tortis. 
Long. (max.) 15-25 ш; lat. s. proc. cire, 7-85 ш; с. proc. 34-47 p ; lat. 
isthm. 4-5 ш; crass. 55 ш. (PI. 6. figs. 19-20.) 
Hab. Yan Yean Reservoir, in the plankton and at the weedy margins ; 
very common in the plankton, Jan. and Feb. 1906 ; abundant among the 
weeds, Mar., Nov., and Dec. 1905. 
The specimens were almost invariably twisted at the isthmus, and the 
processes showed much variation in length. The species bears a considerable 
resemblance to S. tetracerum, Ralfs, but the broad excavation at the apex of 
each semicell and the more horizontally disposed processes easily distinguish it. 
51. Sracrastrum Harpyt, sp. п. (PL 6. figs. 21-22.) 
S. parvum, pene duplo latius quam longum cum processibus, modice 
constrictum : semicellulæ subeampanulatz (vel incudiformes e basi sub- 
angusta), parte basali subeylindrica et angulis basalibus leviter rotundatis, 
apice leviter triundulato, angulis superioribus in processus longos attenuatos 
horizontaliter dispositos productis, marginibus processuum nodulosis, apicibus 
processuum minute tridenticulatis ; a vertice visæ fusiformes, corpore elliptieo, 
polis in processus sublongos rectos attenuatos gradatim productis, marginibus 
processuum undulatis : membrana glabra. 
