616 SOME SYDNEY DESMIDS, 



Long. 50; lat. 40; crass. 24/*. 

 Rose's Lagoon, Collector. 



Var. arcuatum, n.var. (Plate xiii., fig. 4). 



Forma sinu cuneato constricba. Semicellulse basi concava, 

 angulis basalibus late-robundabis, dorso alte-convexo regulariber 

 arcuato, angulis superioribus nullis, granulis in lineas 7-8 trans 

 angulos dispositis, area raediana nuda, etiam apicali. A vertice, 

 semicellulae elliptic* tumidae, granulis in lineas trans versales 

 dispositis, in medio nudse. 



Long. 45; lat. 39; crass. 22/*. 



Collector. 



Cos. mesoleium forma adulta is widespread in this country, and 

 the size constant, from 40 x 30 in young, to 50 x 40 or so in mature 

 specimens. All its forms are larger and longer in proportion 

 than Cos. punctulatum Breb., which, roughly, runs from 20 x 20 

 to 30 x 30, is simply elliptical in end-view and with single pyre- 

 noids. Cos. mesoleium is inflated in end-view, and has double 

 pyrenoids. To this species belong, as Kaciborski has noted, 

 Lewin's two forms (Span. Siissw. T. 1, f. 14, 15), f. malagensis 

 45 x 36, and f. circularis 47-48 x 41-42, crass. 23-24, and Turner's 

 forma rotundata Klebs (Alg. E. Ind. p.54) 40 x 34. 



Cos. Boeckii Wille, var. teifoliatum, n.v»r. (Plate xiii., fig.7). 



Forma paullo major, basi latiore, angulis basalibus acutioribus, 

 lateribus minus convexis, 3-crenabis, brans latera seriebus 3 granu- 

 lorum obscurorum 5-6, granulis singulis (binis 1) infra margines, 

 infra apicem granulis 4, paullo supra centrum papillis 3 in trian- 

 gulum ordinatis. A vertice semicellulae oblongo-elliptica? non 

 tumid*, ubrinque medio tumore piano humillimo instruct*, 

 apicibus late-rotundatis, granulis in seriebus transversalibus. 

 Membrana grosse punctata. 



Long. 34; lat. 32; crass. 18/*. 



Botany (37), Broughton Island (31), common; (Dr. E. Stokes). 



Cf. Cos. Jluviatile Playf., Proc. Linn. Soc. N. S. Wales, 1 907, 

 T.5, f. IS, and Cos. Boeckii var. imperfectum below. The principal 



