150 BRITISH DESMIDIACBJE. 



IRELAND.- -Derryclare Lough, and in lakes, Clifden 

 to Roundstone, Galway ! Near Castlebar, Mayo. 



Geogr. Distribution. Scandinavia. Finland (form). 

 United States (var.). 



This rare and beautiful Desmid is only found in bogs in the 

 region of the older palaeozoic rocks. It is not closely allied to 

 any other British species, but is similar in some respects to St. 

 brachioprominens~Boig. ('Desm. Brasil, 5 1890, p. 952, t. 5, f. 22). 

 Sometimes it is further ornamented with 2 rings of granules near 

 the base of the semicell. Gronblad (' Desm. Keuru ' 1920. p. 70, 

 t. 3, f. 109, 110) records a trigonal form of this species, which, 

 however, seems to differ in other ways from the form originally 

 described. 



144. Staurastrum irregulare West. 

 (PL CXLIX, fig. 7.) 



Staurastrum irregulare West, New Brit. Freshw. Alg. 1894, p. 12, t. 2, f. 49 T 

 50 ; Johns. New Rare Desm. U. S. I, 1894, p. 288. t. 211, f. 10 ; West & 

 G. S. West, Desm. U. S. 1898, p. 314 ; Bohlin, Flor. Algol, d'eau douce 

 d'A?ores, 1901, p. 56, f. 14 ; Gutw. Alg. Ins. Java, 1902, p. 600, t. 40, 

 f. 64. 



Cells small, slightly longer than broad, constriction 

 fairly deep, with a minute median incision ; semicells 

 inversely trapeziform, apex smooth and slightly concave, 

 upper angles produced to form short diverging processes, 

 with denticulate nodulose margins, and bidenticulate 

 apices ; vertical view biradiate, very slightly swollen 

 in the middle, with a truncate and scrobiculate process 

 on each side ; side view of cell fusiform with a deep con- 

 striction, and a scrobiculate process on each side near 

 the base of the semicell. Cells often twisted so as to 

 present a very irregular and distorted appearance. 



Zygospore unknown. 



Length, without processes, 9 '4-9 '6 [JL : with processes, 

 15'3-18'2fjL ; breadth, including processes, 13'5-17'3[JL ; 

 breadth of isthmus 4'8-5'7 [i : thickness 6'6-7'7[i. 



ENGLAND.- -Plankton of Brother's Water. Westmore- 

 land ! Pilmoor, N. Yorks ! 



SCOTLAND. --Rhiconich, Sutherland! Glen Nevis, In- 

 verness ! 



