478 POLYMORPHISM AND LIFE-IIISTORY IN THE DESMIDIACE*, 



According to outline, this really goes under var. repandum, of 

 which it is the forma minor. Its sides are not so sloping as in 

 var. Finmarkice. Var. angustius has the same I'elation to var. 

 repandum that var. cyclopeuvi has to var. Finmarkice, or var. 

 Cambrense to var. notatum. 



Cos. RECTANGULARE Grun., type. 



Long.43; lat.33/x. 



Guildford(60), Auburn(85). 



Var. 7?ii}i?<s( Wille), {Cos. gotlandicum /3 minns Wille, Norges 

 Fersk., p. 31, T.i., f. 13) I have not yet noted, but I think it 

 certainly a var. of rectangulare. From the figures given by Wille 

 and Wittrock, and lately hy W. & G. S. West in their Monograph, 

 it appears that the common form in Europe is depressed in the 

 semicell, while ours are more generally subquadrate. 



Var. FiNMARKl^, n.var. (Pl.xiii., f.I3). 



Forma lateribus e basi plana rapide divergentibus; angulis 

 superioriljus plus minusve rotundatis; apicibus arcuatis. A vertice 

 semicelluifB ellipticpe utrinque inflatte. Long. 38- 42; lat.33-38; 

 crass. 2 2-2 7/i. 



Collector, Canley Vale(llO). 



Develops into var. repandum or var. nodulatum by broadening 

 of the base, the sides becoming less divergent. I had tliis 

 originally down as var. pseicdoprotitbei-ans (Kirchner), but the 

 forms given by Nordstedt, Desm. Gionl., T.7, f.3, and W. &, G. 

 S. West, Monog. iii., Pl.lxxii., f.6-8, certainly belong to Cos. con- 

 tractuni Kirch., as does also the Cos. stdcatuni var. incrassaium 

 AV. & G. S. West, Alg. Ceyl, PI. 20, f.36-38, a form extremely 

 common in this district. The variations of Cos. rectangulare 

 (including sulcatum, etc.) never have an incrassate centre or an 

 open sinus. Cos. coutractam, Cos. ellipsoideum, Cos. foveatum 

 Schm.( = Cos. incrassatum Playf., according to G. S. West), and 

 Cos. pseud oprotnberans Kirch., are young forms of ^r. Bulnheimii 

 Rac.j^Desm. Nowe, T.vi., f. 17) of which Xan. iiiclioatum Nord., 

 . and /3 mammUlatum Playf., are variations. These forms are all 



