486 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACE.E, 



Guildford(60). 



The seraicells become a little more adpressed in the next formy, 

 which develops out of this — hence the cells are a little shorter. 



Var. GRANULOSUM, n.var. (Pl.xii., f.l6). 



Forma semicellulis subreniformibus, sinu angusto introrsum 

 rotundato constricta; angulis lateralibus interdum aculeo minuto 

 prseditis; apicibus interdum levissime deplanatis; lateribus den- 

 ticulationibus minutissimis 3-5 instructis. A vertice semicellulse 

 triangulares; lateribus concavis; angulis inflatis acuminatis aculeo 

 minuto munitis; medio granulis 6 concentrice ordinatis et mediis 

 angulis binis. Membrana minute punctato-scrobiculata. Long, 

 27-28; !at.24-30; ap.8-10; isth.8-10^. 



Guildford (60). 



This form is found sometimes with four denticulations and a 

 spine (or five without) on each side, developing through var. 

 aculeatiim into t\\Q forficulatnm-iovn\; and sometimes with three 

 denticulations and a spine (or four without) growing directly into 

 var. bi/arium forma. 



Var. ACULEATUM, n.var. (Pl.xii., f.l7). 



Forma sinu angusto non lineari constricta. Semicellula3 sub- 

 triangulares, plus minusve adpresste; apicibus minime deplanatis; 

 angulis lateralibus in processum bifidum brevissimum productis; 

 lateribus levissime convexis, aculeis brevibus geminatis binis 

 superiie instructis et interdum denticulationibus supra processum. 

 A vertice semicellulae triangulares, interdum angulis inflati* 

 lateribus concavis, interdum angulis planis lateribus psene aut 

 perfecte I'ectis; apicibus angulorum constrictis, in processum 

 cylindraceum brevissimum productis. Membrana punctato- 

 scrobiculata. Long. c.ac. 34, s.ac. 30-32; lat. c.proc. 32, s.proc. 

 28-30; long, spin.circ. 2; ap. 10; isth. 8-10/i. 



Guildford(60). 



The end-view is at first with inflated angles and hollow sides,^ 

 as in Si. orhiculare; but develops into one with flat sides. At 

 this stage, the end-view much resembles that of St. suhmonticu- 



