BRITISH DESMIDIE^. 173 



at the extremities, which are slightly attenuated and curved downwards ; ends 

 obtuse. Fillets and vesicles none or obscure. 



In a. the empty frond is nearly colourless, and the longitudinal strise are 

 faint. In /3. the colour is deeper and the striae more conspicuous. Trans- 

 verse sutures usually three. 



I have gathered sporangia at Dolgelley and Penzance ; they are orbicular 

 and placed between the deciduous fronds. 



The slender linear frond distinguishes this species. 



Length of frond from yiy to ^ of an inch ; breadth -g-gVo 5 diameter of 

 sporangium -g^ ; distance between the striae xrooo^* 



Length of /3. yjt '■> breadth ^-^ ; length of sporangium -^ ; breadth -g-i-g J 

 breadth between the striae -g^-fyy. 



Tab. XXIX. fig. 6. a. frond of a. with endochrome ; b. empty frond; 

 c, d. sporangia. Fig. 7. a. frond of |3. with endochrome; h. empty frond; 

 c, d. sporangia. 



** Frond striated, much elongated, gradually tapering, scarcehj ros- 

 trate ; sporangium bilobed, situated between the conjugated fronds. 

 17. C. lineatum (Ehr.); frond striated, slender, long, curved, gradu- 

 ally tapering into the conico-rostrate extremities; lower margin 

 slightly inflated at its centre. 

 |3. Longitudinal striae spiral. 



Closterium lineatum, Ehrenberg, Abhandl. der Berlin. Akademie 1833, p. 238 ; 

 Infusor. p. 95. t. 6. f. 8. Meneghini, Synop. Desmid. in Linncea 1840, 

 p. 234. KUtzing, Phijcologia Germanica, p. 131. Jenner, Fl. of Tun- 

 bridge Wells, p. 196. Hassall, British Freshwater AUjce, p. 372. 

 Closterium elongatum, Brebisson, Meneghini, Synopsis Desmid. p. 234 (1840). 



Carnarvon ; Dolgelley ; and Penzance, /. R. Ashdown Forest, and Water- 

 down Forest, Sussex, Mr. Jenner. Aberdeenshire ; and Bauflfshire, Mr. P. 

 Grant. Manchester, Mr. Sidebotham. 



Germany, Ehrenberg, Kutzing. Falaise, Brebisson. Mexico, Bailey. 



Frond large, twelve or more times longer than broad, slightly curved, lan- 

 ceolate, gradually tapering into the slender extremities, which are curved down- 

 wards and obtuse at the end. The upper margin is slightly but uninterrupt- 

 edly convex, so as to form an arc ; the lower margin is concave, owing to the 

 curved extremities, but it is slightly protuberant at the centre. Endochrome 

 reaching nearly to the ends ; fillets three or more, frequently obscure ; vesi- 

 cles in a single longitudinal series. 



Empty frond of a pale straw-colour, with numerous but distinct longitudinal 

 striae, and one or more transverse lines at the centi'e. Specimens occasionally 

 are met with having the striae spirally arranged. This state, which is very 

 beautiful, I can only regard as an accidental variety, as I have observed such 

 a frond conjugated with one of the common kind. 



Closterium lineatum connects the rostrate vdth the other striated species, 

 as in general aspect it agrees vdth some of the latter, and in its inflated centre 

 and tapering extremities with the former. It is liable to be mistaken for C. 

 Ralfsii, but it is longer, more slender, less inflated at the centre, and more 



