30 BRITISH DIATOMACE^. 



W. Sm. 2nd Ser. vol. vii. pi. i. 3. C. Argus, Bail. Obs. pi. ii. 24. 25. ad 

 specimina quae communicavit Prof. "Williamson, Jan. 1852. 



Marine or brackish water. Poole Bay, Nov. 1848. Lewes, 1850, W. Sm. 

 Coast of Norfolk, Mr. Brightwell. (Hudson River.) 



Plate VII. 55. 



6. Campylodiscus parvulus, W. Sm. Valves circular ; canaliculi 

 about 12, minute, in length about two-thirds of radius. Diam. -0011" 

 to -0019". v.v. 



W. Sm. Ann. 2nd Ser. vol. vii. pi. i. 4. Prit. Anim. xxiv. 22, 23. 

 Poole Bay, 1848, JV. Sm. 

 Plate VI. 56. 



7. Campylodiscus Ralfsii, n. sp. V. nearly circular, canaliculi 

 reaching to the median line. Diam. "0016" to •0019". v.s. 



Marine. Ilfracombe, Mr. Ralfs. 

 Supp. Plate XXX. 257. 



Genus 13. SURIRELLA, Turp. 



Frustules free, ovate or elliptical ; valves with a longitudinal central 

 line, and margins produced into alae ; canaliculi distinct, usually 

 parallel. 



The only genus with which the present stands in near alliance is 

 Tryblionella, from which it is well distinguished by the prominency of 

 its alae, the distinctness of its canaliculi, and the usual cuneate form 

 of its frustules : with no other is it at all likely to be confounded. The 

 surface of the valve in Surirella, as in the other Diatomaceee, is marked 

 with transverse lines ; these are usually very faint in the present genus, 

 but in a few cases they are somewhat conspicuous and have been 

 noted in the specific descriptions. 



1 . Surirella biseriata, De Breb. F. V. linear, oblong ; V. elliptical- 

 lanceolate ; alae conspicuous ; canaliculi large, 4 to 6 in 'OOl", 

 usually reaching to central line. Length "0025" to "OOSS". v.v. 



