PROTOCOCCACEJ^. 



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 eeruginous green colour seerus to indicate an affinity with Phycochro- 

 mophycece 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 Eev. M. J. 

 Berkeley on the freestone walls of Christ College, Cambridge." 

 Greville. 



Plate ~K.11. fig. 4. Cells magnified 400 diameters. Some undergoing 

 division. 



ft Tegument thick. 

 Chloxococcum gigas , Grun. in Eabh. Alg., No. 1436. 



Stratum thin, green, mucous ; cells globose, large, either 

 single or associated in small families, always involved in a broad, 

 distinctly laniellose hyaline tegument. 



SIZE. Cells '012--017 mm. diarn. 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 Glceocystis ampla. 



Plate XII. fig. 3. Cells magnified 400 diameters, b, in different stages 

 of division. 



B. Species red, rusty, or orange. 

 No British species in this section recorded. 



Sub-Family 3. POLYEDRIE^E. 



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. Nag. (1849.) 

 Characters the same as above for the sub-family. 



A. Angles entire. 



Polyecbrium gigas. Wittr. Sotvattensalger, p. 33, t. 4, /. 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, b, c, cells in three positions, magnified 400, 

 after Wittrock. 



