BRITISH DKSMIDIEiE. 115 



Aberdeenshire, Dr.Dic/ae aud Mr. P. Grant. Cheshire ; and Ambleside, West- 

 moreland, Mr. Sidebotham. Rochdale, Mr. Coates. 



(3. Penzance and Dolgelley, /. R. 



Germany, Ehrenherg and Kutzinc/. Falaise, Brcbisson. West Point, New 

 York, Bailey. 



Frond smaller than that of Xanthidium acideatum, deeply constricted at 

 the middle ; segments twice as broad as long ; spines subulate, 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. Jenner 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 ^-L- to 3-^ of an inch ; including 

 spines, from 3^ to gJ-j ; breadth, not including spines, from xir^^ ToT 5 ^^^" 

 eluding spines, from -^^ to -^\-^ ; breadth at constriction YsVa- 



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

 not including spines, yJ-^ ; including spines, 3^ ; breadth at constriction y-gVs • 



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. /?. a. front view of frond with endochrome ; b. 

 empty frond ; c. lateral view ; d. end view. 



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

 at the base, the other spines geminate. 



a. Segments reniform ; spines scarcely curved. 

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



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

 uncinate. 



Xanthidium uncinatum, Brebisson, in lit. cum icone (1846). 

 Xanthidium. cristatum j3. uncinatum, Brebisson, in lit. (1846). 



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

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



(3. Ambleside, Westmoreland, Mr. Sidebotham. Dolgelley, J. R. 

 a. and /3. Falaise, Brebisson. 



Frond smaller than that of Xanthidium fasciculatum, 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 m an end one form slight, lateral, 

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

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

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



I 



