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ward and thus gives the frond a curved appearance. The green endochrome 

 is nearly confined to the inflated body. 



Closteriiim Ralfsii may be known from C. rostratiim and C. setaceum by 

 its larger size, the deeper colour of its empty frond, the shortness of its beaks, 

 its firmer texture, and by the upper margin, which, inclusive of the beaks, 

 forms an uninterrupted convexity or arc. 



Length of frond yL of an inch ; greatest breadth g-i^ ; distance between 

 the striae ^rm- 



Tab. XXX. fig. 2. a. frond with endochrome ; b. empty frond. 



19. C. rostratum (Ehr.) ; frond striated, tapering at each end into a 

 setaceous curved beak which is about equal in length to the ventri- 

 cose body ; sporangium cruciform. 



Closteriiim rostratum, Ehrenberg, Abhandl. der Akademie d. Wissensch. zu 



Berlin 1831, p. 67 ; 1833, p. 2 10 ; hifus. p. 97. t. 6. f. 10. Meneghini, 



Synop. Desmid. in Linncea 1840, p. 235. 

 Closterium Acns, Nitzsch, Kiitzing, Synopsis Biatomearum in Linncea 1833, 



p. 595. f. 81 ; Alg. aq. dulc. No. 80. Jenner, Fl. ofTunbridge Wells, 



p. 196. 

 Closterium cmidatum, Corda, Almanack de Carlsbad 183^, p. 125. t. 5. f. 66. 

 Stauroceras Acus, Kiitzing, Phycologia Germanica, p. 133(1845). Brebisson, 



in lit. cum specimine. 



Dolgelley and Penzance, J. B. Sussex ; Kent, 3Ir. Jenner. Durdham 

 Down near Bristol, Mr. Thwaites. Near Congleton, Cheshire ; Ambleside, 

 Westmoreland ; and near Manchester, Mr. Sidebotham. iVberdeenshire, Mr. 

 P. Grant. 



Germany, Ehrenberg, Kutsing, Corda. Falaise, Brebisson. 



Frond lanceolate, tapering into setaceous beaks, which are curved downiwards 

 at the extremity, obtuse at the apex, and nearly equal in length to the inflated 

 body. 



Endochrome green, confined to the inflated portion ; fillets obscure ; vesicles 

 arranged in a single series ; the moving granules are situated at the end of the 

 endochrome, and apparently are not contained within a globule, as their mo- 

 tion has a wider range than in many other species. 



The empty frond is colourless or tinged straw-colour, and the striae are 

 numerous and close. 



Mr. Jenner and myself have gathered conjugated specimens of Closterium 

 rostratum in greater abundance than those of any other species. The cell 

 formed for the reception of the sporangium is intimately connected with the 

 fronds, of which indeed it seems to form a part. When viewed in front it may 

 be described as a four-sided figure, whose angles are cut off at their union with 

 the segments. All its sides are concave, but those between the segments of 

 the same frond are shorter than the others and have deeper and more angular 

 concavities, so that the sporangium has the same figure as the cell. 



Length of frond -^ of an inch ; greatest breadth yoW 5 length of sporan- 

 gium y^j^ ; breadth 3^5^ ; distance between the striae ^sooo - 



Tab. XXX. fig. 3. a. frond with endochrome ; b, d. empty fronds ; c. conju- 

 gated fronds ; e. sporangium. 



