844 AUSTRALIAN FItESHWATER PLANKTON, 



Tetr. spinulosum Schm., forma. (PI. Iviii., f.21). 



Forma pentaedrica; lateribus subplanis; angulis obtusis; spinis 

 tenuibus setis simillimis. Cell. corp. diam. 18/j.. 



Lismore (290). 



Cf. Chodat, Alg. vertes, p.221, f.U7B. This form has the 

 sides ahiiost ilat, the angles obtuse, and very delicate spines like 

 setfe. 



Var. EXCAVATUM, n.var. (PI. Iviii., f.22). 



Forma pentaedrica, valde excavata; angulis radiantibus, coni- 

 cis, baud intlatis, lateribus planis, apicibus modice acutis, spinis 

 tenuissimis instructis. Cell. corp. diam. ca. 20/x. 



Lismore (290). 



In this form, the body is much more excavated on all sides; 

 the cell consists of little moi-e thaii 5, conical, radiating angles, 

 not inflated, but with nearly Hat sides, and rather acute at the 

 apices. Spines very delicate. 



Tetraedron hortensk, n.sp. (PI. Iviii., f.23). 



Cellula; maxima^, wqualiter teti-aedricse ; lateribus levissime 

 concavis; angulis late-rotundatis. Membrana minute punctulata, 

 ad extremos angulos interdum levissime granulata, punctis in 

 seriebus duabus decussatim ordinatis. Cell. diam. 46-72/^. 



Botanic Gai-dens (3, 150); Prospect Reservoir. 



Compare, with this species, Tetr. c/it/as Wittr., Gotl. o. Oelands 

 Sottvattensalg., p. 33, T.4, f.4, and Tetr. tumidtdiim Reinsch, 

 Polyedr. Monog., p.506, T. vi., f.3. The cells are very large, 

 tetraedral, generally with broadly rounded angles, and very 

 slightly concave sides; the angles, however, sometimes tend to 

 be pointed. The membrane is minutely punctate all over, the 

 puncta arranged in decussating lines. 



Tetraedron acutum, n.sp. (PI. Iviii., f.24, 25). 

 Cellulse tetraedricse; lateribus plus minus (ssepe valde) concavis, 

 anguhs protractis; angvilis spinis singulis instructis. 

 Cell. diam. c. sp. 20-34; sp. long. 6-10/x. 

 Parramatta(136); Lismore (258, 259, 263); Enoggera. 

 The cells ai-e tetraedrical; in optical section, triangular, with 



