28 



BRITISH DIATOMA-CE^. 



2. Cyclotella operculata, Kiit;:. V. depressed in centre; striae 

 obscure, very short, 36 in 001". Diam. -0005" to -0012". v.v. 



Ag. Consp. p. 11. Kiitz. Bacill. i. 1. 



Fresh water. Plumpton, Sussex, Mar. 1852, W. Sm. Lough Neagh, 

 Dr. Dickie. Cantyre Peat, &c. 



Plate V. 48. 



3. Cyclotella antiqua, n. sp. V. convex; striae broad, not reaching 

 the margin. Diam. -0009" to -001 3". v.s. 



Fresh water. Lough Mourne and Peterhead Deposits. Cantyre Peat, and 

 Marl, Co. Down. 



Plate V. 49. 



4. Cyclotella Rotiila, Kiitz. V. plane; striae numerous, distinct, 

 14 in -001". Diam. -0015" to -0022". v.s. 



Kiitz. Bacill. ii. 4. Discoplea atmosjiherica, Ehr. in Prit. Anim. xxiv. 1 & 2 ? 

 Fresh water. Lough Neagh, Dr. Dickie. 

 Plate V. 50. 



Genus 12. CAMPYLODISCUS, Ehr. 



Frustules free, saddle-shaped ; valves equidistant ; canaliculi radiated. 



The species included under this genus may all be recognised by 

 the characteristic bend or contortion of their surfaces. The costae, 

 as in Epithemia, appear to arise from the presence of minute canals 

 which form means of communication between the internal cell-mem- 

 brane and the surrounding fluid. In one species, C. cribrosus, these 

 appearances are absent ; but the presence of foramina on the margin 

 in this species seems to indicate the existence of canaliculi, though 

 these are not apparent as distinct costas. 



1. Campylodiscus Horologium, Will. V. circular; canaliculi 

 about 50, in length one-third of the radius ; centre of V. smooth. 

 Diam. -0051" to -0068". v.s. 



Prof. WiUiamson in Ann. Nat. Hist. May 1848. 



Marine. Coast of Skye, dredged in 60 fathoms water by 3Ir. G. Barlee, 

 communicated by Prof. Williamson. 



Plate VI. 51. 



