PROTOOOCCACE. 31 
We have retained this in its present position in deference to Raben- 
horst, to whom the species must have been known. At the same time 
its eruginous green colour seems to indicate an affinity with Phycochro- 
mophycee rather than the present order. 
“ Plant producing spots on walls and stones of a yellowish green colour, 
and at first very small, but afterwards indefinitely larger, from a number 
becoming confluent. First discovered in this country by the Rev. M. J. 
Berkeley on the freestone walls of Christ College, Cambridge.’— 
Greville. 
Plate X11. fig. 4. Cells magnified 400 diameters. Some undergoing 
division. 
+t Tegument thick. 
Chlorococcum gigas, Grun. in Rabh. Alg., No. 1436, 
Stratum thin, green, mucous; cells globose, large, either 
single or associated in small families, always involved in a broad, 
distinctly lamellose hyaline tegument. 
Sizz. Cells ‘012-017 mm. diam. without the hyaline mem- 
brane. 
Protococcus gigas, Kutz. Phy. Gen. p. 145. 
In pools, on walls and glass windows. 
One of the finest species in this genus, and possibly not uncommon. 
We have met with it two or three times, but not in any great quantity. 
It must not be confounded with Gleocystis ampla. 
Plate XII, fig. 3. Cells magnified 400 diameters. 6, in different stages 
of division. 
B. Species red, rusty, or orange. 
No British species in this section recorded. 
Sub-Family 3. Poyuprize. 
Cells single, segregate, free swimming, compressed, 3-4-8 
angled ; angles more or less produced, sometimes radially elon- 
gated, either entire or bifid, mostly armed, oblong-elliptic when 
viewed laterally, rounded or rather truncate at the ends. Cell- 
membrane thin, even. Chlorophyll-mass mostly granular, 
equally distributed through the cell, sometimes with 1-4 reddish 
oil-drops. Propagation unknown. 
Genus 24. POLYEDRIUM. WNég. (1849.) 
Characters the same as above for the sub-family. 
A. Angles entire, 
Polyedxium gigas. Wittir. Sotvattensalger, p. 33, t. 4, f. 4. 
Cells irregularly pentahedrical (rarely hexahedrical), angles 
obtuse, sides concave. 
Size. Maximum diameter of cells -065-075 mm. ; minimum 
diameter °035-"045 mm. 
Archer, in Quart. Journ. Micr. Science xvii. (1877), p. 105. 
In standing pools. 
This large and distinct species has the angles rounded and unarmed. 
Plate XIII. fig. 1. a, 6, ¢, cells in three positions, magnified 400, 
after Wittrock. 
