200 B1UT1SH DESMIDIACExE. 



than broad, very deeply constricted, sinus narrowly 

 linear with a dilated extremity; semicells broadly 

 pyramidate-truncate, basal and upper angles rounded, 

 sides slightly convex, apex wide and straight or 

 very slightly convex ; cell-wall granulate, granules 

 large, not quite uniform in size, those in the centre of 

 the semicells and near the basal angles and lateral 

 margins generally somewhat larger than the others, 

 with 7-9 granules visible on each lateral margin, those 

 near the apex usually smaller than those at the base, 

 apex smooth (destitute of marginal granules), granules 

 with no definite disposition, but scattered at equal 

 distances, sometimes in very indistinct oblique series, 

 with some minute scrobiculations surrounding the 

 granules in the centre of the semicells ; cell-wall 

 between all the granules densely and very minutely 

 punctate. Side view of semicell circular, granules of 

 lateral margins very prominent, apex smooth. Vertical 

 view elliptic, ratio of axes about 1 : 1*65, with the 

 granules at the middle on each side rather larger than 

 the other marginal granules, in the centre with a 

 punctated area destitute of granules. Chloroplasts 

 axile, with two pyrenoids. 



Zygospore globose, wall furnished with a number of 

 strongly convex circular thickenings (" bull's-eyes "), 

 about 7 or 8 of which are visible at the margin. 



Length 50-59 /< ; breadth 42-56 //, ; breadth of isth- 

 mus 18-16//,; thickness 28-30 /.i; diam. zvgospore 

 52-5-61 ,i. 



ENGLAND.- -Cumberland ! Westmoreland ! (ItisseM), 

 at 2400ft. on Helvellyn ! Lancashire ! W., X., and 

 E. Yorks ! Cheshire (with zygospores, Roi/). Leicester- 

 shire (Poi/). Cambridgeshire! Warwickshire! (Wills). 

 Middlesex ! Surrey (zygospores from Thursley 

 Common)! Kent! Hants! (Bennett). Wilts! Devon! 

 Cornwall! (Half*; Mxrqiuind). Monmouth ! 



WALES.- -Fairly general in Carnarvonshire and 

 Merioneth ! Radnor ! 



SCOTLAND. General ! Common in the Outer 



