OF THE DESMIDIE.E. 



725 



T. Amei'icanum (nobis). — Frond 



broader than long, suborbicular, pinna- 



tifid; lateral lobes separated from the 



terminal by a deep acute incision, hori- 



j zontal, conical, tapering, their extremities 



i bidentate ; end lobe short, its lateral pro- 



! jections long, tapering, bidentate at their 



j extremities, as broad and long as the lateral 



I lobes ', ends broadly rounded. = Micras- 



j terias incisa (Kiitz.), Bailey, in ^Micr. 



I Obs. in S. Carolina,' &c., but surely not 



j that species ; we are therefore obliged to 



place it here under another specific 



I name. 



I T. pinnaiijiduni (Dixon). — Frond ra- 



j ther broader than long, plane, pinnatifid ; 



I lateral lobes separated from the terminal 



I by an equal subacute incision, triangular, 



subcouical, horizontal, their extremities 



bidentate ; end lobe short, its lateral 



projections transverse, short, bidentate 



at the extremities, ends straight (colour 



pale). L. 1-440"; B. 1-392''. = 3//c;-as- 



terias pinnatijida (Ealfs, Breb.) ; Euas- 



truin pinnatifiduni (Kg.). G.B.,'F., G., 



U.S.A. 



T. didymacanthum (Nag. sp.). — Frond 

 about as broad as long, pinnatifid ; late- 

 ral lobes separated from the temiinal by 

 a icide rounded sinus, their lower margin 

 convex, in apposition with those of the 

 opposite segment for a portion of their 

 length, then slightly divergent, their 

 upper margin nearly straight, horizontal, 

 their extremities bidentate ; end lobe 

 long, united to the basal portion by a 

 naiTow neck, its lateral projections short, 

 their extremities bidentate, ends slightly 

 convex. L. 1-40'" ; B. 1-40"'. = Euas- 

 t?'um didymacanthum (Nag.). G. 



T. quadratum (Bail. sp.). — Frond 

 broader than long, pimiatifid, quadran- 

 gular; lateral lobes separated from the 

 tenninal by a wide rounded sinus, some- 

 what injiated at their base, elongate, 

 slightly divergent from those of the 

 opposite segment, their produced extre- 

 mities slender, bidentate ; end lobe nar- 

 row, produced, its lateral projections 

 transverse, elongate, slender, bidentate 

 at the extremities; ends vdi\\ a slight 

 central conca\dty. = 3Iic. quadrata (Bail.), 

 U.S.A. 



* Extremities of lobes entire, mucronate 

 or acute. 

 Tetrachastrum arcuatum (Bailey, 

 sp.). — Frond rather broader than long, 

 pinnatifid, quadrangular ; lateral lobes 

 long, slender, arcuate, tapering, divergent 

 from those of the opposite seginent, their 

 extremities acute ; tenninal lobe narrow, 

 produced, its lateral projections uhruptly 

 transverse, slender, attenuated, acute ; 

 ends slightly concave at the centre. 



= Micrasterias arcuata (Bail.). U.S.A. 

 T. expansutn (Bailey, sp.). — Frond 

 about as broad as long, somewhat stel- 

 late ; lateral lobes long, slender, straight, 

 conical, divergent from those of the op- 

 posite segment, their extremities acute ; 

 terminal lobe narrow, produced, its la- 

 teral proj ections somewhat divergent, short, 

 quickly tapering, acute; ends concave. 

 = 3Iicr. expansa (Bail.). U.S.A. 



T. mucronatum (Dixon). — Frond 

 longer than broad, subelliptic ; lateral 

 lobes very broad, straight on the margin 

 forming the base of the segment, tnrgid 

 on the upper margin, their extremities 

 rounded, fm-nished on the margin with 

 one, two, or three minute mucro-like spifies, 

 one always at the exti'emity or basal 

 angle of the segment, others, when pre- 

 sent, in-egularly placed on the upper 

 margin ; terminal lobe short, very broad, 

 its lateral projections short, stout, 

 quickly tapering, somewhat incmwed at 

 extremities, which are mucronate ; ends 

 rounded, with a very shallow inconspi- 

 cuous centi'al concavity; tr. v. broadly 

 elliptic; e. f. pimctate. L, 1-167"; B. 

 1-235". I. 



2 * Extremities of the lobes bidentate. 



T. oscitans (Dixon). — Frond about as 

 broad as long, pinnatifid; lateral lobes 

 separated from the terminal by a rounded 

 sinus, horizontal, conical, their extremities 

 bidentate ; end lobe short, broad, its 

 lateral projections short, conical, usually 

 bidentate, narrower and shorter than the 

 lateral lobes ; ends convex at the centre ; 

 tr. V. fusiform, e. f. punctate. L. 1-256" ; 

 B. 1-211". (II. 28, '^).=Euastrum 

 holocystis (Kg.); Holocystis oscitans 

 (Hass.) : Micrasterias oscitans (Ralfs). 

 G.B., I., F., U.S.A. 



Genus MICRASTEEIAS (Ag.). — Frond mostly lenticular, as long as or 

 slightly longer than broad, deeply constricted into two lobed segments ; seg- 

 ments usually semiorbicular, 5- or sometimes 3-lobed ; lobes incised or 

 divided, mostly radiant, narrower at the base and ividening upivards, their 

 ultimate subdivisions spreading, dentate or minutehj spined, or rarely only 

 sinuate at the outer margin ; central constriction usually linear. 



