152 BRITISH PESMIDIACEJE. 



Zeitschr.' 1906, no. 2, p. 6) in regarding this species as a 

 form of St. Clepsydra Nordst. 



1 7. Staurastrum Clepsydra Xordst. 

 (PL CXXII, fig. 6.) 



Staurastrum Clepsydra Nordst. Desm. Brasil. 1870, p. 224, t. 4, f. 47 [a 

 obtusum and (3 acuminatutn] ; -Lagerh. Bidr. Amerik. Desm.-fl. 1885, 

 p. ^46; De Toni, Syll. Alg. 1889, p. 1139; Hoy & Biss. Scott. Desm. 

 1893, p. 179. 



Cells small, as broad as long or a little broader ; 

 very deeply constricted, sinus widely open, sub- 

 rectangular or acute-angled ; semicells obversely 

 subtriangular, sides convex, apex straight or convex, 

 angles very slightly produced and sometimes sub- 

 mucronate. Vertical view triangular, sides very 

 slightly concave, angles very little rounded and some- 

 times submncronate. Cell-wall smooth. 



Zygospore unknown. 



Length 27-31^; breadth 2 7-3 6 /x; breadth of 

 isthmus 6-8 p. 



SCOTLAND.- -A clinerran in Logie-Coldstone, Aber- 

 deen (Hoy fy Bissett). 



Geogr. Distribution.- -Norway. Sweden. Poland. 

 Spitzbergen. Greenland. United States. Brazil. 



The characters of this species are a little obscure, and we 

 have not personally seen any Desmid exactly agreeing with 

 Nordstedt/s original figure. We are, however, acquainted 

 with a small Desmid, described by Borge in 1891 as " St. 

 sibericum," which we think cannot with justice he separated 

 from St. Clepsydra. 



Var. sibericum (Borge) nob. (PL CXXII, figs. 7, 8.) 



Staurastrum sibiricmn Borge, Bidr. Siber. Chlor. ]891, p. 9, t. 1, f. 4 

 [forma ovalis] \Y. & G. S. West, Further Contrib. Freshw. Plankton 

 Scott. Lochs, 1905, p. 502, t. 7, f. 20; Brit. Freshw. Phytoplankton, 

 etc., J 909, p. 1 83. 



Cells smaller and less deeply constricted. Vertical 

 view fusiform or triangular. 



Forma OVALIS Borge, 1. c. Vertical view fusiform, 

 poles slightly rounded and almost imperceptibly pro- 

 duced. Length 17-20 n ; breadth 17-21 //; breadth of 

 isthmus 7*5-8*5 u thickness 8-9 i. 



