632 Wisconsin Academy of Sciences^ Arts, and Letters. 
Tetraedron trigonum (Nageli) Hansgirg. 
Hedwigia 27: 130. 1888. 
III. Rice (rrr). 
Tetraedron verrucosum sp. nov. 
Cells four-angled, with convex sides, tetrahedric or with the 
two sides crossed over one another. Angles obtuse, with a thick 
projection 13-18/x long. Wall thick, verrucose. (Plate 15, figs. 
1 - 2 ). 
Diam. cells 65-80 /x. 
The shape of the cell is at times like T. re^gulare Ktz. but T, 
verrucosum differs in its larger size and verrucose walls. The 
warts on the walls are more pronounced than in any other species 
of the genus. 
III. Bear (rr). 
Tetraedron proteiforme (Turner) Brunnthaler. 
In Pasclier, D. Siisswasserfl. Deutschl., osterr. u. d. Sehw. 5: Chlorophyceae 
2: 152. /. 177. 1915. 
Polyedrium yroteiforme Turner, Kgl. Sv. Vet.-Ak. Haudl, 25: No. 5: 
158. pi. 20, /. 24B, 1892. 
Turner states that the cells may be either two or three-angled, 
but no two-angled cells were observed in the Wisconsin collec¬ 
tions. This species forms a connecting link between the genera 
Tetraedron and Cerasterias. (Plate 15, figs. 4-5). 
II. Paddock (rrr). 
III. Lac Court Oreilles (rr). Rice (rrr). 
Tetraedron enorme (Palfs) Hansgirg, 
Hedwigia 27: 132. 1888. 
Stdurastrum enorme Ralfs, Brit. Desmidieae 140. pi. 33, -figs, lla-lle. 
1848. 
III. Devils (r). 
Tetraedron lobulatum var. polyfurcatum Gt. M. Smith. 
Bull. Torr. Bot. Cl. 43: 480, pi. 26, figs. 21-22. 1916. 
III. Beaverdam (rr), Rice (rr), Shell (rrr). 
