BY G. I PLAYFAIR. 119 



Every length, in successive increments of 2 /x, between 22 /x 

 and 88 fx, was actually observed and measured. The frustules 

 were in long ribbons, the shorter ones (long. 22 ji and upward) 

 being quite as broad as the longest (or even broader) were very 

 unlike Synedra in appearance. 



Genus Surirella Turpin. 



SuRiRELLA ovALis var. PiNNATA (W. Sm.) Van. Heurck. 



Long. 30-40; lat. valv. 10-12, ap. 3-4; lat. frust. 8-12 /x. Costse 

 5-6 in 10/x. 



Lismore(3, 12,22). (PL iv., f.39, 40). 



Syn., ^uri. lapponica Astrid Cleve, Recent Frw. Diat., p. 25, 

 PL i., f.26. S. ovalis type also noted (long. 44-48, lat. 26 /x, costse 

 18-20 a side) in Nos.2, 3, 11. 



Var. Lbvvisii mihi. (PL iv., f.41-43). 



Valvse facie inflata ; membrana media distincte marginata; 

 costai breves, validae, lateribus parallelis, ad marginem merabranse 

 abrupte terminatse. 



Long. 50-64; lat. valv. 32 /x. 



Lismore(5). 



Cf. Suri. ovalis Lewis, Diat. U. S. seaboard, p. 63, PL 1, f.3. 

 Lewis calls it " a sparangial form." Var. Lewisii has the same 

 relation to the type that Cyclotella Mcneghiniana /S (var. coiivexa 

 mihi, infra) has to its type. The costie are convex and terminate 

 abruptly at the edge of the central smooth membrane. In this 

 form they increase in number by new ones forming between the 

 others, growing from the edge outwards. Usually in Surirella 

 the new marginal costse, verrucse or denticulations form at the 

 apices, the latter being the growing points of the frustule. 



Surirella plana G. S. West, forma. (PL v., f.l). 



Long. 100-134; lat. valv. max. 44-50; lat. frust. ap. 36-48, bas. 

 24-30 /x. 



Verrucas marginales circ. 20; latere cingulato ut in Suri. 

 rohustd. 



Lismore. Cum sequenti rarius. 



