BY G. I. PLAYFAIR. 479 



• commonly incrassate in the centre of the semicell; and never 

 have a linear sinus, but always an open one, or, at most, one 

 with parallel sides. Compare the Cos. coiitractian in Rac, Desm. 

 Polou., T.X., f. 10. The development of the latter also is from 

 the top downwards; the broad truncate apex tends to remain and 

 become broader. In Wille's pseudoprotuberans,{ = var. cyclopeum 

 Playf., forma) which is certainly a variation of Cos. rectangidare, 

 the semicell develops from tlie base upwards, the truncate apex 

 being continually obliterated. Wille's form is said(Monog., iii., 

 ip.TO) to be a variation of Cos. protii^berans Lund., and this I 

 think very probable. The latter, then, must be considered a 

 variation of Cos. rectangulare, a form indeed smaller than any I 

 have yet observed, but Gutwinski has recorded the type as low 



■ down as 28 x 25. Like Cos. protuherans Lund., all these 

 recta7igula7-e-v a.ria.tions have a minutely and closely punctato- 

 scrobiculate membrane, not always so evident as in my figures, 



• but always visible. Relying, therefore, on the evidence of Nord- 

 stedt and W. & G. S. West, I have relegated the name j^seudo- 

 protiiherans to Cos. conlractum. But my form in Pl.xiii., f. 13, is 

 manifestly(38-42 x 33-38) the f. major of Wille's specimen(33 x 27) 

 and is certainly identical with the '■'■ forma angidis superioribus 

 semicellularum rotundalis" of Borge, Norska Finmark, p. 12, 

 f. 10, upper semicell. I have, therefore, given it the name var. 

 Finmarkice. 



Var. ROTUNDATUM, n.var. (Pl.xiii., f.l7). 



Forma var. Finmarkice angulis superioribus valde rotundatis. 

 Semicellulai subreniformes; lateribus e basi plana divergentibus, 

 minimo spatio rectis; angulis lateralibus laterotundatis; dor.so 

 latissime et perfecte arcuato, Membrana punctato-scrobiculata. 

 Long.38-42; lat.32-3(.i; crass.21; istli.8/x. 



Guildford(114), Canley Vale(llO). 



This form, of whose connection there is no doubt, affords an 

 excellent example of the smoothing down of a characteristic 

 feature in the stress of cell-division. In the smaller forms com- 

 pare var. reniforme and var. suhreniforme. 



