nRlTISH DESMIDIE/E. 115 



Aberdeenshire, Dy. D/c/v> aiulMr. P. Grant. Chesliire ; and Ambleside, West- 

 moreland, Mr. Sidebof/iom. Rochdale, Mr. Cuatcs. 



/3. Penzance and Dolgelley, J. R. 



Germany, E/trenberff and K'utzing. Falaise, Brehisson. West Point, New 

 York, Bailey. 



Frond smaller than that of Xanthidium acideatum, deeply constricted at 

 the middle ; segments twice as broad as long ; spines subidate, slender, ge- 

 minate and marginal, in general slightly curved, but occasionally straight. 

 Each segment commonly has only four pairs, though sometimes six. The 

 central projections are conical, inconspicuous, to be detected only in end and 

 lateral views, and even then liable to be overlooked. A mucous covering can 

 usually be detected in a, but I am doubtful of its presence in /3. 



The variety /3. Mr. Jenncr considers nearer to Xanthidium Brebissonii than 

 to X. fasciculatum ; but, in my opinion, it agrees better with this species in 

 size, and especially in the shape of the central projections. 



Length of frond, not including spines, from -j\^ to -^^ of an inch ; including 

 spines, from 3^ to ^^ ; breadth, not including spines, from -^\-^ to -^^ ; in- 

 cluding spines, from -^^ to -^\-^ ; breadth at constriction y-gVs- 



Length of var. /3, not including spines, j^t ; including spines, -^^ ; breadth, 

 not including spines, -^^ ; including spines, 3^ ; breadth at constriction Y9V3 • 



Tab. XX. fig. 1. a. front view of frond with endochrome ; b. front view of 

 frond with mucous covering ; c. empty frond ; d. transverse view ; e. lateral 

 view. 



Tab. XIX. fig. 4. var. /3. a. front view of frond with endochi'ome ; b. 

 empty frond ; c. lateral view ; d. end \'iew. 



5. X. cristatum (Breb.) ; segments with a solitary spine on each side 

 at the base, the other spines geminate. 



a. Segments I'eniform ; spines scarcely curved. 

 Xanthidium cristatum, Brebisson, in lit. (1846). 



/3. uncinatum, Breb.; segments truncate at the end; spines 

 uncinate. 



Xanthidium uncinatum, Brebisson, mi /^7. cum icone (1846). 

 Xanthidium cristatum /3. uncinatum, Brebisson, in lit. (1846). 



a. Not uncommon. Dolgelley and Penzance, J.R. Ambleside, Mr. Side- 

 botham. Aberdeen, Mr. P. Grant. Pulborough, Sussex, 3Ir. Jenner. 



13. Ambleside, Westmoreland, Mr. Sidebotham. Dolgelley, /. E. 

 a. and p. Falaise, Brebisson. 



Frond smaller than that oi Xanthidium fascicidatum, the spines subulate and 

 marginal ; each segment has four pairs, and on each side of the base a solitary 

 one ; the central elevations, which are less distinctly granulate in a. than in /3, 

 are scarcely -visible in a front view, but in an end one form slight, lateral, 

 conical projections, the pearly granules encircling them like a necklace. In o. 

 the segments are subreniform and all their spines nearly straight. The seg- 

 ments in j3. are about equal in length and breadth, the ends being truncated, 



I 



