BRITISH DESMIDIE^. 163 



^ Sporayigium orbicular, situated between the conjugating fronds and 

 but slightly connected with them ; fronds never rostrate. (Closte- 

 rium.) 



t Frond semilunate or semilanceolate, tapering from the middle, the 

 lower margin straight [or nearly so) and inclined upwards at the end. 



1. C. Lunula (Miiller) ; frond smooth, semilunate; lower margin nearly 

 straight, inclined upwards at the rounded ends ; vesicles numerous, 

 scattered. 



Vibrio Lunula, Miiller, Naturforsch. p. 142 (1/84) ; Animal. Infus. p. 55. 



t. 7. f. 13 and 15. 

 MuUeria Lunula, Leclerc, Mem. du Mus. I. (1802). Schrauk, Faun. Boica, 3. 



p. 47. 

 Bacillaria Lunula, Schrank, Acta N. Cur. 11. p. 533 (1823). 

 LunuUna vulgaris, Bory, Encyclop. Meth. Hist. Nat. des Zooph. t. 2 (1824). 



Turpin, Bid. cFHist. Nat. t. 5. 

 Closteriutn Lunula, Ehr. et Hemprich, Symb. Phys. 1828, t. 2. Ehr. Abh. der 



Berl. Ak. 1830; Infus. p. 90. t. 5. f. 15. Kutzmg, Alg. aq. dulc. 



No. 22 ; Synopsis Diatom, in Linncea 1833, p. 596. Corda, Aim. de 



Carlsbad, 1835, p. 190. t. 5. f. 56 and 57. Jenner, FL of Tunbridge 



WeUs, p. 196. 



Common. Carnarvon; Dolgelley; Penzance, &c., /. iJ. Several stations 

 in Sussex, Kent, and Surrey, Mr. Jenner. Kerry, Mr. Andrews. Aberdeen- 

 shire, Dr. Dickie and Mr. P. Grant. Near Congleton, Cheshire ; Ambleside, 

 and near Manchester, Mr. Sidebotham. 



Germany, Kiitzing, Ehrenberg, Corda. Falaise, Brebisson. Common in 

 New York and New England; Mexico, Bailey. 



Frond bright green, stout, distinctly visible to the naked eye, semilunate, 

 five or six times longer than broad ; extremities conic with rounded and very 

 obtuse ends. The upper margin is very convex, the lower straight, except at 

 the extremities which incline upwards, so that the segments rapidly taper from 

 their junction. Endochrome grass-green ; fillets several, three more distinct 

 than the rest ; vesicles numerous, small and scattered. 



The empty frond is colourless and without markings, and its suture is indi- 

 stinct or wanting. It shrinks in drying, and is destroyed by burning. 



Closteriutn Lunula differs from C. Ehrenbergii and C. moniliferum in having 

 no inflation at the middle of the lower margin ; and although, in drying, it 

 often acquires a prominent centre, its upward inclination at the extremities is 

 a permanent mark of distinction. It may be known from C. acerosum by its 

 stouter appearance and scattered vesicles. 



I have never seen a specimen in which the length exceeded the breadth so 

 much as in Ehrenberg's figure. 



Meneghini refers C. Lunida of Kutzing's * Alg. Aq. Dul.' to Closterium mo- 

 niliferum ; but two specimens which I have had an opportunity of examining, 

 one in a copy of that publication, and another given me by Kiitzing himself, 

 belong to this species. I have therefore followed Ehrenberg in considering 



M 



