0¥ THE DESMIJ)IE^. 



741 



e.v. with three broadly rounded crenated 

 angles, sides nearly straight, each with a 

 slight shaUoiv depression or constriction at 

 the middle. F. 



S. (dternans (Breb.). — Segments in f. v. 

 elliptic or oblong, two or three times 

 as broad as long, separated by a wide 

 sinus, tivisted, unequal ; rough with very 

 minute pearly granules ; e.v. with three 

 ohtiise and rounded angles, forming short 

 not colourless rays, alternating with 

 ''those of the other segment, sides con- 

 cave. L. 1-1037" ; B. 1-1106';. (ii.l6,17.) 

 = Goniocystis (Tri(/onocystis) hexaceros 

 (Hass.), k dispar (Breb.) ? G.B., I., 

 R, U.S.A. 



S, dilatatum (Ehr.). — Segments in 

 f. V. fusiform, their lateral extremities 

 obtuse, equal, rough with puncta-like 

 pearly granules j e.v. "^dth four rotmi' 

 dato-truncafe angles, forming short, 

 broad, not colourless ravs, sides concave. 

 L. 1-1201"; B.1-1S81". ^Phycastrum di- 

 latatum (Kg.), Goniocystis (Staurastrum) 

 dilatata (Khss.). G.B., I., F., G., Italy, 

 U.S.A. 



S. cre7iatum (Bailey). — Segments in 

 f.v. fan-shaped in oidline, separated by a 

 wide rounded sinus, inner margin concave, 

 smooth, outer semicircular, crenate ; e.v. 

 with three rotundato-truncate crenate 

 angles, sides concave, smooth. U.S.A. 



7* Segments with or without spines; in 

 f V. with spines {if any) few and scat- 

 tered; in e. V. angles emarginate or 

 hijid, or truncate and the extremities 

 plane and quadrangular. 



S. hifidum (Ralfs). — Segments in f.v. 

 . . . . ; in e.v. with three acidely hijid or 

 emarginate angles, the teeth acute ; sides 

 concave. = Desmidium hifidum (Ehr.), 

 Phycastrum hifidum (Kg.), nee Gonio- 

 cystis (S.) bifida (Hass.). F., G. 



S. quadrangidare (Breb.). — Segments 

 in f.v. subquadrate, with a few short 

 bifid or tooth-like spines spreading later ally, 

 otherwise smooth : e.v. with four tru7i- 



cate and emarginate angles ; sides concave. 

 L.1-1157"; B. 1-1163". (in. 24, e.v. 25.) 

 /3, angles in e.v. broader, with/o?^r teeth 

 at the extremity, and tivo minute teeth on 

 upper side (Breb.). G.B., F. 



S. Cerberus (Bailey). — Segments in f.v. 

 truncato-oblong, smooth; the opposite 

 lateral extremities abruptly truncate, ex- 

 ternally plane and quadrangular, the an- 

 gles drawn out into acute spine-like ex- 

 tensions or teeth, two projecting upwards 

 and two downwards ; e.v. with three 

 abruptly truncate angles, extremities as 



in f.v. plane and quadrangular, the teeth 

 at the angles divergent. U.S.A. 



8* Segments ivithout spines; in f.v. and 

 e.v. the angles te^'ininated by either a 

 conspicuous rounded nipple-like projec- 

 tion, or an enlarged rounded knob, or 

 an elongate cajntate process. 



S. tumidum (Breb.). — Segments in f.v' 

 elliptic, turgid, smooth ; their margin 

 striated, and their opposite lateral ex- 

 tremities furnished with a rounded con- 

 spicuous nipple-like p>rojectio7i ; e.v. with 

 three or fom- angles, the nipple-like pro- 

 jection terminating the angles, sides 

 convex ; e. f. punctate ; gelatinous in- 

 vestment very evident. L. 1-200" : B. 

 1-250". = /^. orbiculare (INIenegh.), Phyc- 

 astrum tumidum (Kg.). G.B., I., F. 



S. glohulatum (Breb.). — Segments in 

 fv. fusiform, capitate; e.v. with three 

 angles, each enlarged into a rounded 

 granulated knob, sides nearly straight, 

 (ill. 26, e.v. 27.) F. 



S. bacillare (Breb.). — Segments in f.v. 

 somewhat arcuate, each diver gent from the 

 opposite segment, somewhat attenuated, 

 Jinally capitate, smooth; e.v. with from 

 three to five capitate Y?ijs,.= Phycastrum 

 bacillare (Kg.). F. 



9 * Segmetds in fv. with the opposite 

 lateral extremities each tapering into a 

 single more or less elo7igate colourless 

 process divided at the apex, which in 

 e. V. terminates the angles, with or with- 

 out intermediate simple or truncate 

 spi?ies. 



t Segments smooth. 

 S. brachiatum (Ralfs). — Segments in 

 f.v. smooth, narrow below, widening up- 

 wards, ends truncate, the lateral extre- 

 mities each produced into a smooth, elon- 

 gate, straight, tapering, divergent process, 

 bifid or trifid at the apex; e.v. tri- or 

 quadriradiate, sides concave. L. 1-1111"; 

 B. 1-1785". = Goniocystis (S.) bifida 

 (Hass.), Phycastrum Ralfsii (Kg.). G.B,, 

 I., F., G. 



2t Segments rough \vdth superficial 

 granules, those on the processes ar- 

 ranged in transverse lines. {S. poly- 

 morphum has sometimes a few incon- 

 spicuous scattered spines.) 



S. tricorne (Breb.). — Segments in f.v. 

 somewhat fusiform, often twisted, rough 

 with minute puncta-like granules, taper- 

 ing at each side into a short usually co- 

 lourless process, blunt, or divided at the 

 apex ; e.v. tri- or quadriradiate, processes 



