178 SOME NEW OR LESS KNOWN DESMIDS FOUND IN N. S. WALES, 



Genus Arthrodesmus Ehr. 

 Ar. ellipticus, 11 sp. (T.iv. f.4-5). 



Ar. magiius, subcircularis, medio sinu cuneato, aperto, intror- 

 suin rotundato, constrictus. Semicellulae circ. 2^plo. latiores 

 quam longae, ellipticae vel subhexagonae; angulis lateralibus 

 obtusis in aculeos singulos productis; aculeis brevibus validis 

 plus minus assurgentibus; a vertice visae late ellipticae, apicibus 

 acumiiiatis et in aculeos singulos protractis, medio utrinque area 

 incrassata. Membrana punctata, crassa, semper in medio semi- 

 cellularum (sed non evidente) interdum ubique (aculeis etiam) 

 valde, incrassata. 



Long. 42, 44, 48, 48, 48, 52; lat. 66, 65, 57, 60, 60, 70; crass. 24, 

 28, 2Q^. 



Ptose's Lagoon, Collector; Botany. 



The spines are relatively short, almost dentate in young forms, 

 and generally form a continuation of the dorsal margin. The 

 large iucrassate spot in the centre of the semicells distinguishes 

 this species from Ar. convergent^, to some forms of which it is 

 similar in shape and size. The incrassation of the membrane, 

 including the spines, in old specimens is quite a feature of this 

 form. Cf. Xan. tetracentrotuni Wolle, in W. & G. S., West N. 

 Am. Desm. T. 15, f.24; Ar. incrassatus Lager., Am. Desm. f.l8; 

 Ar. gibberulus Josh., in Journ. Bot. 1885, T.254, f.6; and Ar. 

 curvatus Turn., Alg. E. Ind. T. 1 2, f.2. 



Genus X A N T H I D I u M Ehr. 

 X. ocTONAKiuM Nord., Alg. N. Z. p.42, T.4, f.22. 



Long. c.ac. 100, 112, 108, 104, 102; lat. c.ac. 85, 78, 90, 88, 82; 

 long. s.ac. 76, 82, 78, 78, 72; lat. s.ac. 60, 58, 56, 54, 56; long. acul. 

 15, 15, 16, 17, — ; crass. 40, 37, — -, — /x. 



6 + 66 + 77 + 7 6 + 6 6 + 7 

 ' ^P"^^« 6T6 ^T7 7T7 6^ ^T7 



Botany. 



It is truly remarkable that I have never yet come across a 

 specimen with the full eight pairs of spines to the semicell. All 



