BRITISH DIATOMACE^. 69 



W. Sm. Ann. 2n(l Ser. vol. ix. p. 1 2. pi. ii. 15. Prit. Anim. xx. 15. Naviciila 

 Spencerii, Quekett on the Microscope, pi. ix. 



Fresh water. Near Lewes, Sept. 1850, W. Sm. Reading, Mr. C. Poulton. 



Plate XXII. 218. 



Genus 23. SYNEDRA, Ehr. 



Frustules attached, elongate, rectangular ; valves linear or lanceolate, 

 plane or convex. 



In the present genus the frustules, though often found in a free 

 state, are at first invariably attached to larger Algae, or other plants, 

 by a cushion-like pedicel, which, in a few cases, becomes developed 

 into a more or less distinct stipes. In some species the frustules, 

 after self-division, are speedily detached from this gelatinous cushion, 

 which in such cases rarely presents us with more than two or four 

 individuals, as in S. lunaris. In others, the frustules, after repeated 

 division, still remain adherent to their pedicel ; and the result is a 

 fan-like band of frustules, as in S. pulchella, or a stellate cluster, 

 as in S. radians. The valves are usually furnished with a central 

 pseudo-nodule and median line, the extremities of which are slightly 

 dilated ; but these characters are variable, and not unfrequently ab- 

 sent, and are therefore inadmissible in the generic description. 



Sect. I. Pseudo-nodule obsolete or very minute ; frustule arcuate. 



1. Synedra lunaris, Ehr. V. narrow, linear, slightly attenuated, 

 obtuse; striee 36 in -001". Length -0025" to -0038". v.v. 



Ehr. Inf. xvii. 4. Kiitz. Bacill. xiii. i. 5. xv. 1. Prit. Anim. iv. 185. Exi- 

 laria lunaris, Hass. Alg. xcvii. 4. 



Fresh water. Boggy pools, Dorsetshire, Dec. 1849 ; near Lewes, Nov. 

 1852, W. Sm. Coldbath Spring, Tunbridge Wells, Mr. Jenner, Apr. 1842. 

 Lancashire, Mr. Johnson, Apr. 1852. 



Plate XI. 82. 



2. Synedra biceps, W. Sm. V. linear, inflated at the obtuse extre- 

 mities; striae 48 in -001". Length -0042" to -0075". v.v. 



Emiotia Jiexuosu, Kiitz. Sp. Alg. \^. (J. ad specira. authen. qme misit cl. 

 De Brebisson, Jan. 1853. 



