STAURASTRUM. 5 



A form with the cell-wall minutely punctate ; in all 

 other respects quite similar to the type. 



ENGLAND. Bowness, Westmoreland ! Thursley Com- 

 mon, Surrey ! 



IRELAND. Near Westport, Mayo ! Clifden and Bally- 

 nahinch, Galway ! Adrigole, Cork ! 



Var. circulare Turn. (PL CXXIX, fig. 16.) 



*S7. DirJcieiv&r. circulare Turn. Fresh w. Alg. E. India, 1893, p. 105, t. 16, f. 5 ; 



West & G. S. West, Some X. Amer. Desm. 1896, p. 255. 

 St. Dickiei var. semicirculare West & G. S. West, Alg. S. England, 1897, 



p. 492. 

 St. brevispinum Hustedt, Desm. Bac. Tirol, 1911, p. 338, f. 28. 



Cells nearly circular in outline, not quite so deeply 

 constricted as in the type ; semicells nearly semicircular, 

 sinus linear in the median part, finally opening more 

 widely. Spines straight and considerably shorter than 

 in the type, very strongly inflexed, and attached at the 

 basal angles of the semicell. 



Length 24-40 \L ; breadth 26-40 p ; breadth of isthmus 

 8-12 (JL ; length of spines 2-3 JJL. 



ENGLAND.- -Thursley Common, Surrey ! 



Geogr. Distribution. --Poland. India. Central Africa. 

 United States. 



This variety is well defined from the type by reason of its 

 semicells with, very strongly convex apex and short, straight, and 

 strongly inflexed spines, which project from the basal angles of 

 the semicell. 



Var. rhomboideum West & G. S. West, (PL CXXIX, 



fig. 17.) 



-67. Dickiei var. rhomboideum West & G. S. West, Scott. Freshw. Plankt. I, 

 1903, p. 545, t. 16, f. 9. 



Semicells distinctly rhomboidal in shape ; spines 

 rather longer, and strongly incurved. 



Length 37 pi ; breadth, without spines, 38 '5-46 [JL ; 

 length of spines 6-9 'opt ; breadth of isthmus 8 '5 pi. 



SCOTLAND.- -Plankton of Loch nan Eun, N. Uist, 

 Outer Hebrides ! 



