40 THE FLORA OF NEBRASKA. 



Xantliidinm fasciculatum Ehrb. Inf. 1836. 



Half-cells with four, rarely six, pairs of long, subulate, marginal, spreading 



spines, central projection minute, conical, not beaded; diameter 55-63 fi, 



length 60-80 fi without spines. 

 Minden. PI. VI., Figs. 13 and 14. 



9. PLEl ROTAENIOPSIS Lundell. Desm. Suec. 511. 1871. 



Cells short, cylindrical or rotund, more or less constricted in the middle, even 

 divided into two half-cells; chloroplasts arranged in two parietal longi- 

 tudinal bands, their margins irregularly lobed and furnished with many 

 pyrenoids. 



Etymology: Pleurotaenium and oipig, appearance. 



Plenrotaenopsis ralfsii (Breb.) Lund, 1. c. 



Cosmarium ralfsii Breb. in Ralfs Brit. Desm. 1848. 



Cells orbicular or suborbicular, deeply constricted, sinus narrow; half-cells 

 subtriangular, inferior angles obtuse, dorsum high convex; membrane 

 smooth or finely punctate; diameter 60-100 /j.; length 70-120 /n. 

 South Bend. PI. VII., Fig. 6. 



10. COSMARIUM Corda Alman. de Carlsb. 205. 1835. 



Cells short, cylindrical, round, or elliptical, always constricted in the center, 

 not spiny, margin often undulate or crenate, apex more or less rounded 

 or truncate; chloroplasts radiate, 1-2 in each half -cell; membrane 

 smooth, verrucose or granulate, not spinose; zygospore globose, spinose 

 or rarely smooth and angular. 



Etymology: Greek noa/uapiov, chain. 



Section I.— Central part of cell not ventricose. 

 Sub-section 1. — Chloroplasts single in each half cell. 



Cosmarinm granatum Breb. in Ralfs Brit. Desm. 96. 1848. 



Minute, longer than broad, both ends truncate, constriction linear; half-cell 



a triangular trapezoid; cells 22-46x18-30 /j.; constriction half the 



diameter. 

 Minden. PI. VII., Fig. 7. 



Cosmarinm biocnlatnm Breb. in Ralfs Brit. Desm. 95. 1848. 



About as long as broad or slightly longer, constriction deep, producing a 

 broad notch on each side; half-cells compressed, oval, with a convex 

 base, obtusely rounded at the apex, entire or slightly crenate; membrane 

 smooth or minutely punctate; zygospores orbicular, covered with coni- 

 cal spines, 12-30x10-20 //. 



Thedford. PI. VII., Fig. 11. a, b, c. 



Cosmarinm leve Rabh. Fl. Eur. Alg. III. 1868. 



Longer than broad, very smooth, constriction deep, sinus narrowly linear; 

 half-cells with high rounded ends, usually somewhat refuse; membrane 

 finely granular; diameter 14-16 fi, length 20-26 n. 



Var.— septentrioiiale Wille Ferskvandslager fr. Novaja Semlja 43. 1880. 



Broader than the type; half-cells in side view ovate-circular; diameter 22 v, 

 length 28 [i. PI. VII., Fig. 3, a, b, c. 



