BRITISH DESMIDTE.E. 177 



Frond very minute, five to eight times longer than broad, slender, slightly 

 curved ; extremities attenuated ; ends blunt, but frequently one more so than 

 the other. The figure of the frond is variable ; the upper margin is more or 

 less convex, the lower one concave or straight ; occasionally the extremities 

 curve in opposite directions. Endochrome very pale. Vesicles wanting ac- 

 cording to jMcneghini ; but INIr, Jeimer informs me that they are present, 

 although indistinct. The empty frond is colourless. 



]\Ir. Jenner has gathei'ed conjugated specimens at Rackham Bogs. The 

 sporangium, which is quadrate, is large compared with the size of the plant. 

 The empty segments of the frond remain attached to the angles of the spo- 

 rangium. 



Closterium Cormi differs from C. acutum in its obtuse ends. 



Length of frond -^^ of an inch ; breadth -j^Vg • 



Length of (j. ^4^ ; breadth a^O" '■> length of sporangium -^\^ to -^\^ ; 

 breadth -pfL_ to ^. 



Tab. XXX. fig. 6. a, b. fronds of /3. with endochrome ; e, d. front views of 

 sporangia ; e. side view of sporangium \ f, y. fronds of a. 



22. C acutum (Lyngbye) ; frond curved, gradually tapering at each 

 extremity ; end more or less acute ; empty frond colourless. 



a. Frond six to twelve times longer than broad ; ends subacute. 



EchineJla acuta, Lyngbye, Tent. Ilydrophytologice Danicce, p. 209. t. G9. G. 



(1819). 

 Frustulia acuta, KUtzing, Synopsis Diatomearum in Linncea 1833, p. 537. 

 Closterium acutum, Brebisson, in lit. cum icone (1845). 

 Stauroceras acutum, Brebisson, in lit. (184G). 



/3. Frond ten to twenty times longer than broad, tapering at each 



extremity into a very fine point. 



Frustulia subidata, Kutzing, Synop. Diatom, p. 538. f. 3 (1833). 

 Stauroceras subulatum, Brebisson, in lit. cumicone (1846). 



Dolgelley and Penzance, J. R. Rochdale, 3Ir. Coates. Brightling near 

 Battle, Sussex, Mr. Jenner. 



Germany, KUtzing. Falaise, Brebisson. 



Frond very minute and slender, many times longer than broad, narrow-lan- 

 ceolate or acicular, slightly curved, gradually tapering ; extremities hyaline, 

 and more or less acute at the apex. Vesicles obscure ; fillets none ; endo- 

 chrome \ery pale, and not extending to the extremities. The moving granules 

 are free, and more or less remote from the ends. 



The empty frond is quite colourless and free from markings. 



Sporangia are not uncommon. I have frequently gathered them at Dol- 

 gelley and Penzance, and M. de Brebisson has sent me drawings of French 

 specimens. The sporangium is cruciform in the front and oval in the side 

 view. It is inclosed in a cell, similar to itself in form, but extending beyond 

 it at the angles into the adjoining portion of the respective segments. In their 

 empty state the segments have so much the colour and appearance of the 

 water in which they are immersed that it is diflScult to trace them, and the 



