122 DESMIDS OF THE UNITED STATES. 



margins of the other lobes also, provided with a few scat- 

 tered spines. The figures of two semi-cells show consider- 

 able variation in the arrangement of the spines and divisions 

 of lateral lobes. 



Diameter 140-150 /*., without spines; length 200-210 yu. 

 Collected near Minneapolis, Minn., by Miss E. Butler. 



SECTION II. Cells subelliptlc; semi-cells three or five lobed; lobes radiate, the 

 end lobe somewhat exserted, divided and arms divergent. 



M. FURCATA, (Ag. ), Ealfs. Plate XXXIX, figs. 5, 6. 



Cells five lobed; lobes bifid, their divisions linear, diver- 

 gent, and forked at the apex. The end lobe exserted, its 

 divisions divergent, producing a wide, shallow sinus. 



Diameter 150-180 yu. ; Common. 



Var. SIMPLEX, Wolle. Plate XLVII, figs. 6, 7. 



Cells equal in length and breadth, two lobed, terminal 

 lobe exserted, its divisions spreading and producing a wide, 

 shallow sinus ; lateral lobes usually simple, but sometimes 

 divided into two narrow, linear diverging sections, furcate 

 at apices. Length and breadth 140-150 /<. 



A singularly variable species. Of the thirty-one fresh speci- 

 mens examined during a stay at Winter Park, Florida, by 

 Rev. H. D. Kitchel and myself, twenty were found of normal 

 form as upper half of fig. 6, 7, no arms divided ; five had all 

 the lateral arms divided, like the lower half of figure ; one 

 had two arms divided and two single, like figure ; two had 

 only one arm divided, and three had each two arms divided. 

 As two-thirds of the forms examined had all the arms single, 

 this is considered the type ; the others, one-third, variable, 

 are varieties. 



M. PSEUDOFURCATA, Wolle. Plate XXXIX, fig. 4. 



Five lobed, simple, not bifid ; sometimes the lateral lobes 

 appear more like one bifid lobe on each side ; in either case 

 only half as many lateral arms as characterize the preceding 

 species, M.furcata. 

 Diameter 150-160 yu. 



Not as frequent as the true form, but it has a habitat in 

 many localities in the Middle States. 



Tar. MINOR, Wolle. Plate XLI, fig. 11. 



Small, not one-half the diameter of the typical form, but 

 so nearly like it in outline, I note it as a variety. Had but 

 two or three specimens, from Minneapolis, Minn. 



