7(> BRITISH DESMIDIACE^E. 



l.ivjulth. without spines, 60 [i ; with spines, 65 [i ; breadth 

 of isthmus 17'5{JL. 



SCOTLAND. Corrie Ceandor, Perth ! 



( .1. Staurastrum Ravenelii Wood. 

 (PI. CXXXVITI. figs. 7, 8.) 



St. /.'"<< nelii Wood, Freslnv. Alg. N. Amer. 1873, p. 153, t. 21, f. 22 ; Wolle, 

 Desm. I . S. 1SS4, p. 143. t. 45, f. 17, 18, t. 52, f. 7, 8 ; De Toni, Syll. 

 Alg. 1889, p. I 17-J : \\Vst \- G. S. West, Some Desm. U. S., 1808, p. 312. 



Si. Tri U-h use Turn. Desm. Notes, 1893, p. 345, f. 12 ; Nordst. in Wittr. 

 \ \..rUt. Al.tr. exsic. no. 1477, and fasc. 35, 1903, p. 11. 



Cells small, about as long as broad or a little longer, 

 dreplv constricted, sinus linear for some distance, then 

 .pi'iiing more widely; semicells subelliptical or sub- 

 reniform. or even subpyramidate - truncate, dorsal 

 mnruiii much more convex than the ventral, basal angles 

 broad I v rounded. Cell- wall provided with conical 

 i:r; mules, arranged in rather distinct concentric circles 

 round the angles, and sometimes becoming emarginate, 

 about 8 or 9 rows visible across the face of the semicell. 

 Vertical view triangular, lateral margins nearly straight,, 

 granules wanting in the centre of the apex. 



Xyii'ospore unknown. 



Length 28-36 p ; breadth 28-32^ ; breadth of isth- 

 mus 8-14(i. 



WALES. Trelleck Common, Monmouth (W. B. Turn.). 

 Distribution. -Sweden. United States. 



It is si i M ;,_,-, . s ted amongst the notes of the late Professor West that 

 . Ti-rHrckmse Turn, is synonymous with St. Ravenelii Wood. 

 Although the figures of Wolle, Wood, and Turner are all poor, 

 certain similarities are evident, for they seem to represent a small 

 Stawastrum with oval or elliptical semicells, lateral angles 

 broadly rounded, and with the cell-wall covered with acute 

 < cincal granules (The error in Wolle, ' Desm. U. S.' 1884, t. 45, 

 is pointed out by the author himself.) The alga distri- 

 buted in Wittr. cV- Xnrdst, ' Alg. Exs.' no. 1477, as a form of 

 Tretteckense Turn, seems to differ in several points from the 

 plant Bgurecl l.v the above authors, cf. PL CXXXVIII, figs. 7, 8. 

 semicells are more depressed, and instead of being more 



