150 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



a specific place on the cell. The present circumscription of the assemblage is 

 essentially that given by Senn (1900, pp. 117-118), who removed the Rhizo- 

 mastigaceae (placed here by Klebs) to the Pantostomatineae and added certain 

 families, among others the Tetramitaceae, which Klebs had placed in his group 

 Polymastigina. Since the time of Senn, Lemmermann (1914, pp. 52-121) and 

 Huber-Pestalozzi (1941, pp. 280-301), among others, have given treatments of 

 the group. It is comprised of the following families. 



Family Trypanosomaceae Doflein orth. mut. Lemmermann (1914, p. 64) 



Family Bicoecaceae Stein orth. mut. Senn (1900, p. 121) 



Family Craspedomonadaceae Stein orth. mut. Senn (1900, p. 123) 



Family Phalansteriaceae Senn (1900, p. 129) 



Family Bodonaceae Biitschli orth. mut. Engler (1898, p. 7) 



Family Cryptobiaceae Lemmermann (1914, p. 107) 



Family Amphimonadaceae Kent orth. mut. Engler (1898, p. 7) 



Syn.: Spongomonadaceae Stein orth. mut. Engler (1898, p. 7) 

 Family Trimastigaceae Kent orth. mut. Senn (1900, p. 141) 

 Family Tetramitaceae Kent orth. mut. Engler (1898, p. 7; see Skuja, 

 1948, p. 68) 

 ?Family Paramastigaceae Skuja (1948, p. 68) 



Distoniatineae : This group was first established by Klebs (1892, p. 329) as a 

 subgroup Distomata of his group Polymastigina. The present circumscription 

 of the Distoniatineae is essentially that of Senn (1900). He removed some of 

 the forms which Klebs had placed in the Polymastigina to the Protomastigineae, 

 abandoned the group Polymastigina, and elevated the Distomata to a group of 

 major rank. (See Doflein, 1928, who retains the Polymastigina and credits it 

 with seven families, p. 620.) 



The forms placed in this small group are characterized, among other fea- 

 tures, by the double nature of the individuals — the body consisting of two halves 

 and usually possessing two nuclei, two sets of flagella, and two oral fissures. 

 (For a discussion on the occurrence of synzoospores in the algae in general, in- 

 cluding the Chrysophyceae, and a comparison of them with representatives of 

 the Distomatineae, reference should be made to two papers by Pascher: 1929, 

 1939.) 



All the representatives of the Distomatineae are placed in the family Disto- 

 mataceae (Klebs) Blochmann orth. mut. Engler (1898, p. 7). 



CLASS BACILLARIOPHYCEAE 



Characterization: This class is comprised of uninucleate, diploid, unicellular and 

 colonial, unattached (mostly free floating) or attached forms in which the inner part of 

 the wall of the cell (known as the frustule) consists of pectin and the outer part of sili- 

 ceous material. The wall is composed of two halves, one of which, the epitheca, is slightly 

 larger and overlaps the other, the hypotheca. Each theca is in turn always composed of 

 at least two pieces — the somewhat convex valve which is attached at its edges to the 

 connecting band. It is the two connecting bands that overlap slightly, and together they 

 constitute what is known as the girdle. In a number of forms the depth of the frustule 

 is increased by the formation of one to many (depending upon the species) intercalary 

 bands between the valves and their connecting bands. 



The valves are usually elaborately sculptured whereas the ornamentation in the con- 

 necting bands is ordinarily much less conspicuous. The sculpturing is due to perforated 

 thin areas (chambers) in the siliceous material (cf. Kolbe, 1948, pp. 4-12; Desikachary, 



