BY G. I. PLAYFAIR. 183 



Very like certain forms of St. Dickiei and St. dejectum. See 

 St. Dickiei in Wolle, T.40, f.5, var. circnlare Turn., Alg. E. Ind. 

 T.16, f.5, forma Borgesen C. Braz. T.4, f.42, St. dejectum var. 

 converyens Wolle, T.40, f.21, and Ar. hiatus Turn., I.e. T.ll, f.34. 



St. okbicularr Elir. (i denticulatum Nord., Desm. Cent. Braz. 

 T.4, f.42. (T.iv. f.l4). 



Forma lateribus ad basin retractis, angulis basalibus interdum 

 denticulis singulis instructis. Membrana valde incrassata prae- 

 cipue ad angulos et ad apicem, den.se punctata. A vertice angulis 

 rotundatis, papillis latis singulis praeditis. 



Long. 50-54; lat. 42-50;^. 



Botany. 



Cf. St. orh.ii verruco sum Wille, Norges Fersk. p. 40, T.2, f. 26, 

 which is about half the size. The above form is not exactly like 

 either of the two cited, but is like a cross between them. St. 

 denticalatum has no papillae at the angles in end view, and St. 

 verrucosum does not show the strongly incrassate angles viewed 

 from the front. The tooth from which the Brazilian form takes 

 its name is not always present in Australian specimens either. 

 Nordstedt's fig. (I.e.) works out at 50 x 42/n. 



St. pseudobiretum, n.sp. (T.iv. f.l5). 



St. mediocre, fere tam longum quam latum, medio sinu brevi 

 lineari constrictum, isthmo lato. Semicellulae trapezoideae, dorso 

 dimidioquam basi latiores; angulis inferioribus obtusis; lateribus 

 rectis e basi divergentibus; angulis superioribus acuto-rotundatis; 

 dorso levissime arcuato. Anguli superiores granulis obscuris in 

 seriebus obliquis transversalibus 5 ornati; apicibus denticulis 

 binis interdum munitis. Semicellulae a vertice triangulares, 

 angulis acutis leviter inflatis, seriebus 5 transversalibus granu- 

 lorum ornatis. 



Long. 50-54; lat. dors. 52-GO; lat. bas. 30-40/z. 



Murray's Lagoon, Collector. 



The first view reminds one of Cos. hiretum., of which a var. 

 trlquetruiii with tln-ee rounded angles in end view is recorded 



