STAURASTRUM. 137 



Cells small, usually a little broader than lono\ includ- 



/ o^ 



ing the processes, deeply constricted, sinus acute and 

 widely open ; semicells almost globular, dorsal margin 

 convex, ventral margin much more turgid ; angles 

 produced to form short, stout, and strongly inflexed 

 processes, tipped with 2 or 3 minute spines and provided 

 with several concentric series of denticulations, which 

 become stronger more remote from the apices of the 

 processes, so that the apex of the semicell seems to be 

 spinous in the front view. Vertical view triangular, 

 sides slightly concave, angles rather acutely rounded, 

 with 3 or 4 series of denticulations, centre of apex smooth, 

 with a small but prominent spine just within each 

 lateral margin at the middle point. Cells usually 

 twisted at the isthmus. 



? Zygospore unknown.* 



Length 17-23^ ; breadth, without processes, 10-12 (JL; 

 with processes, 20-23 \L ; breadth of isthmus 5-7 y. . 



ENGLAND.- Near Senen, Cornwall ! 



\\ ALES.- -Llvn Idwal, Carnarvonshire ! 



i 



SCOTLAND. Aberdeen, Kincardine, Forfar and Perth 

 (Eoy & Biss.). 



IRELAND.- -Dublin and Wicklow (Arch.). 



Geoyr. Distribution.- -France. Switzerland. Sweden. 

 Franz Josef's Land. 



This species is not at all common. It is closely allied to St. 

 polymorphic in, but is distinguished by its very strongly inflexed 

 processes, and the stronger spine-like denticulations. 



137. Staurastrum eboracense Turn. 

 (PL CXLIII, fig. 23.) 



Staurastrum eboracense Turn. Desm. Xotes, 1893, p. 345, f. 1J. 



Small, with 4 incurved arms, rounded at the ends ; 

 each arm with 3 or 4 rows of conical granules ; sides 

 sinuate ; sinus rounded. It has an apical corona of 

 little verruca? ; remainder, except arms, smooth (Turner). 



Zygospore unknown. 



* Cf. footnote p. 109 (St. inJJexum). 



