STAUKASTKUM. 161 



23. Staurastrum Cosmarioides Nor (1st. 

 (PL CXXV, figs. 11, 12.) 



Staurastrum Cosmarioides Nordst. Desm. Brasil. LS70, p. 223, t. 4, f. 4-: 5 ; 

 Alg-. Brasil. 1877, p. 23 : De Toni, Syll. Alg. 1889, p. 1194 ; Borg. Desm. 

 Brasil. 1890, pp. 49, 50, f. 1-6 [formael ; W. & G. S. West, Some Desiu. 

 U. S. 1898, p. 313 ; Alga-fl. Yorks. 1901, p. 103. 



Cells of various magnitudes, generally of medium 



. 

 size or rather large, about twice as long as broad, 



deeply constricted, sinus linear ; semicells semi-elliptic, 

 or subpyramidate, sides convex (rarely faintly concave 

 in the middle), apex a little flattened and slightly 

 thickened. Vertical view trigonal (or rarely tetra- 



O t 



gonal), with broadly rounded angles and very faintly 

 retuse sides. Cell- wall punctate. 



Zygospore unknown. 



Length 64-142 p.; breadth 39-62 p,; breadth of 

 isthmus 14-34 p.. 



EXGLAXD.- -BlubberliouseSjW. Yorks (IT. B. Turner}. 

 Xew Forest, Hants ! 



SCOTLAND.- -Ben Chiurn, Perth! 



(rfoyr. Distribution.- -United States. Guiana (var.). 

 Brazil. 



A number of somewhat varied forms have been figured by 

 Borgesen as examples of this species. It is possible that all 

 the records of St. Cosmarioides refer to trigonal and tetragonal 

 forms of species of Cosmarium akin to C. pyramidatum and 

 C. pseudopyramidatum, but further investigations are neces- 

 sary to decide this point. St. Cosmarioides is one of those 

 connecting-links between the genera Cosmarium and Stau- 

 rastrum, and without doubt originated in the former genus. 

 In parts uf the American continent it appears to have become 

 well established. 



24. Staurastrum tortum (Lagerh. & Nordst.) nob. 



(PI. CXXV, fig. 9.) 



Cosm a r ii'.m tortum Lagerh. & Nordst. in "VVittr., Xordst., & Lagerh. A 1^-. 

 Exsic. 1903, n<>. I486 ; fasc. 35, p. 16, f. 1-8. 



Cells very small, a little longer than broad, con- 

 spicuously twisted at the isthmus, slightly constricted, 

 VOL. iv. 11 



