— 168 — 
Long. 674—858 4; lat. ad bas. semicell. 334; lat. ad med. semicell. 
28; lat. ad apic. semicell. 35. (Tab. nostr. Il, fig. 1). 
The tubercles, which are situated just below the apex, were about 
24 in number. They are much less conspicuous than the tubercles of 
many other Plewrotenia of this nature, and consist of somewhat slight 
plications of the cell-wall at the apex. In fact, the tubercles of all Plew- 
votenia of this nature are primarily due to a series of short (but pro- 
minent) foldings or plications round the apex. In a few species these 
plications are surmounted by actual bead-like outgrowths, but this is not 
often the case. 
In stagnant water among Spirogyra decimina var. 
Area: India. 
45. VP. trochiscum West & G.S. West in Trans. Linn. Soc. bot. 
ser. 2, V, 1896, p. 235, t. XIII, f. 4,5; cfr. Journ. Linn. Soc. bot. XXXII, 
1898, p. 285—286. 
Long. 335—468 4; lat. ad bas. semicell. 383—42y; lat. ad apic. 
semicell. 26—29 ys. 
The Siamese specimens differed from the American ones in being a 
little thicker towards the base of the semicells. In the character, arrange- 
ment and number of the markings they were absolutely identical. 
In stagnant water in the jungle, and in muddy ricefields, abundant. 
Area: N. America, Ceylon. 
46. P. hypocymatium West & G.S. West |. c. 1896, p. 234, 
t. XU, f. 1. 
Forma paullo major, undulis paucioribus eis ad basin majoribus. 
Long. 451 w; lat. ad bas. semicell. 19 #; lat. ad apic. semicell. 12,5 pz. 
The Siamese specimens were a little longer than the American ones 
and the undulations did not extend so near the ends of the semicells. 
As the basal undulation was also a little larger than the others the Plev- 
rotenium bore a certain amount of resemblance to P. basiundutum West 
& G.S. West. 
In stagnant water. 
Area: N. America, Ceylon (var angustum). 
Euastrum Ehrenb. 
47. E. ansatum Ehrenb.; Ralfs Brit. Desm. 1848, p. 85, t. XIV, f. 2. 
In muddy ricefield. 
Area: Ubiquitous. 
48. K, sinuosum Lenorm. in Ralfs 1. c. p. 85, t. XII, f. 5 a, b, d. 
E. circulare Hass. 
Long. 61 ys; lat. 39 4; lat. isthm. 10 py. 
In stagnant water. 
A small form was observed somewhat approaching var. reduetum 
