BRITISH DESMIDIE/E. 135 



Phycastrum tricorne, Kvitzing, Phycoloyia Gennanica, p. 137 (1845). 



Dolgelley and Penzance, J. R. Ambleside, Mr. Sidebotham. Cross-in- 

 Hand, Sussex, M?-. Jenner. 



/3. Penzance, J. R. Near Pulborough, Sussex, Mr. Jenner. 



Falaise, Brebisson. Germany, Ehrenberg, Kutzing. 



Frond about as large as that of Staurustrum alternans, deeply constricted 

 at the middle ; segments in the front view somewhat fusiform ; in an end one 

 showing three or four blunt, generally entire angles. 



The segments are frequently more or less twisted, in which case this plant 

 bears a close resemblance to Staurastrum alternans ; but I retain the species 

 in deference to the authority of M. de Brebisson ; the tapering of the seg- 

 ments at their sides is however its chief distinction. 



The sporangia, which I have gathered at Penzance, are orbicular, and fui-- 

 nished with spines divided at the apex. 



Length of frond yytt ^^ ^^^ i"^^ ' breadth gJ-g- ; breadth at constriction 

 3^ J- ; diameter of sporangium -^-^ ; length of spines xxry- 



/3. Length of frond from y o' oo ^^ qtt 5 breadth from y^^ to ^-iy ; breadth 

 at constriction -^-^^ ; diameter of sporangium ^^ ; length of spines 3-53-3 • 



Tab. XXn. fig. 11. a,b. front views of frond ; c. end view. 



Tab. XXXIV. fig. 8. a. sporangium ; b. front ^-iew of var. /5 ; c. end view ; 

 d. sporangium. 



tt Angles terminated by minute spines or tapering into slender 



pi'ocesses^. 



25. S. polymorphum (Breb.) ; segments rough with minute granules, 



having on each side a short process tipped with spines ; end view 



three- to six-rayed. 

 Staurastrum polymorphum, Brebisson, in lit. (184fi). 



Dolgelley, J^.jK. Reigate, Surrey ; and near Pulborough, Sussex, Mr. Jenner. 



Falaise, Brebisson. 



Frond much smaller than that of Staurastrum gracile, deeply constricted 

 at the middle ; segments irregular in form, but generally broader than long. 

 Each side terminates in a short truncate projection or process, which is 

 scarcely longer than broad, and tipped by three or four distinct, diverging 

 spines ; frequently there are also a few inconspicuous scattered spines on the 

 segment itself. The number of the angles or rays in an end view varies from 

 three to six, but the four-rayed form is the most abundant. The size of the 

 frond is proportionate to the number of these rays. 



The sporangia, which I have gathered at Dolgelley, are orbicular ; their 

 spines are few and forked at the apex. I have seen three-rayed fronds coupled 

 with four-rayed ones. 



* A variety of Staurastrum tricorne has the angles tipped by minute spines, 

 and occasionally Staurastrum cyrtocerum is destitute of spines, excepting those 

 terminating the processes ; both forms would therefore be referred to this section. 



