SOME XORTH AMERICAN DESMIDIE.E. 2i3 



This species is not imfrequent, hut has not heen placed on record for the U.S., as tliat 

 which was described and figured hy Wolle (Desm. U.S. p. 102, pi. 2i. ivj;. 1-5) is now 

 known as U. TFollei, Lagerh. 



.53. ErASTRUM ATTENUATUM, Wollc, Desm. U.S. p. 103, pi. 26. fig. 17. (E. UasHngsii, 



WoUe, Desm. U.S., new edit. p. 113, pi. 42. figs. 10, 17, et Wolle in lit. cum 



icone.) (PL XIY. figs. 20, 21.) 



Having seen a large number of specimens of this species, we feel confident that tJio 



above two species of "Wolle are the same ; aod as neither his figures nor descriptions 



under either name represent this characteristic species, we feel it necessary to descril)e 



and figure the true plant. 



U. mediocre, subcluplo longius quam latins, profunde constrictum, sinu line^iri; 

 semicellulse trilobcie, angulis inter lobos rectangularil)us et rotundatis, lobis Interalibus 

 retusis,lobulis sfepe leviter emarginatis,iis inferioribus projicientioribus, lobis])olaribus 

 elongatis (l§-plo longioribus quam latis), lateribus levissime divergentibus, apicibus 

 levibus et subtruncatis cum angulis rotundatis, infra et juxta apicem plicatis; intra 

 lobos laterales (inter lobulos) tumore singulo et in centro semicellulae tumoril)us 

 binis verticaliter dispositis instructis ; a vertice visae ellipticae tumore singulo ad 

 apicem unumquemque et lateribus tumoribus tribus utrobiquc, lobo polnri circulari 

 et crenulato ; a latere visae partibus inferioribus subrectangu lares lateribus retusis, 

 tumoribus 4 intus cruciatim dispositis, lobis polaribus ut a fronte visis. 

 Long. 61-63 /tt; lat. 36-5-38-5 a*; lat. lob. pol. 11-11*5 ^u; lat. isthm. 11-5-13-5 ^t; 

 crass. 21-22 At. 



The lateral lobes are not rectangular as figured by Wolle, but in all the specimens the 

 margins converge somewhat, so that the upper lobule does not project so much as the 

 lower one. The polar lobe is about the same length as in Wolle's figure of E. attenuatum, 

 but certainly longer than that figured for E. Hastingsii. The apex is perfectly smooth 

 (and is not crenulate as figured by Wolle for both E. attenuatum and E. Eastingsii) ; 

 the longitudinal plications are on a dilated portion just below the apex, which gives a 

 somewhat crenulated appearance to the apex when the plant is slightly tilted. 



64. E. EVOLUTUM, nobis. (PI. XIV. fig. 2*2.) 



E. ahruptnm, Nordst., var. cvolutimi, Nordst. in Ofvers. Sv. Vet.-Akad. Forh. (1877) 

 n. 3, p. 2], t. 2. fig. 7. 



E. NorcUtedtiamim, Wolle (ex parte), Desm. U.S. pi. 26. figs. 7, 9, 11, 12. 



This species is an abundant one in the material we have examined ; although it is 

 somewhat variable, its distinctive characters are always retained. 



Above the denticulate protuberance on each side of the polar lobe there is always a 

 stout spine, which, however, varies much in length ; the lower of the two divisions of the 

 lateral lobes is always the larger, and usually has a few more teeth. On each side of the 

 sinus there is always present a large granule ; above the central protuberance there are 

 two very distinct scrobiculations, and within the margin on each side of the polar lobe 

 there is always a rounded or emarginate wart. 



The figures given by Wolle for E. Nordstedtianum are evidently intended to represent 



