l^esmidiece.] Infusorial animalcules. 265 



hrachiatum. In end view S. Ivcve is unlike any other species. Lengtk 

 1- 1220th. 



(G.) — Drond rottgh, with puncta^like granules. 



t ^nd view with entire, rounded or truncate angles or short rays, 



Staurastrum alternans. — Segments rough ; with pearly granules ; 

 narrow, oblong, and, from their twisted position, unequal in the front 

 view ; end view triangidar, with the angles of one segment entire, 

 and alternating with those of the other. (P. 13, f. 16, 17.) 



S. alternans may be Icnown from S. dilatatum and S. punctulatum 

 by its unequal segments in the fi'ont, and alternating angles in the 

 end view. Sporangia orbicular, with spines forked at the apex. 

 Length 1- 1037th. 



S. punctulatum. — Segments rough, with puncta-like granules, 

 elhptic, equal; end view triangular, ■with broadly rounded angles 

 and slightly concave sides. 



In S. rugidosum the pearly granules are larger and fewer, and at 

 the angles appear like little spines. Length 1- 704th. 



S. dilatatum, (Ehr.) — Segments rough, fusiform, equal; end view 

 quadrangular, with four short, broad, truncate and entire rays. 

 Frond very minute ; deeply constricted at the middle ; the sinuses 

 rounded. (P. 2, f. 100, 101.) It differs from S. alternans in not 

 being twisted ; its rays also (in an end view) are more truncate. 

 Length l-1201th. 



S. margaritaceum = Pentasterias ma/rgaritaeea, (Ehr.) — Eough, 

 tapering at the constriction, and having short lateral processes ; end 

 view with five or more short, narrow, obtuse rays. (P. 2, f. 104.) 

 Length 1-1 176th. 



S. tricorne = Desmidiiim hexaceros, (Ehr.) — Rough, with puncta- 

 Hke granules; tapering at each side into a short, blunt, mostly 

 entire process ; end view with thi-ee to four blunt angles. 



Var. fb.J — Processes terminated by minute spines. (P. 2, f. 99.) 

 It frequently bears a close resemblance to S. alternans from the twist- 

 ing of its segments ; the tapering of the segments at their sides is 

 its chief distinction. Sporangia orbicular, with spines divided at 

 the apex. Length l-1275th to l-948th. 



f f Angles terminated by minute spines, or tapering into slender 



