BRITISH DIATOMACE^E. 101 



PODOCYSTIS, Bail. Nov. Gen. 



Frustules attached, sessile, cuneate ; valves convex, obovate, striated ; 

 with a median line and transverse costae. 



The transverse costae or canaliculi distinguish this genus from 

 Podosphenia; its attached growth and moniliform striae from Surirella. 



72. Podocystis Americana, Bail. Striae moniliform, 30 in -001"; 

 costae 12 in -001". Length of F. -0016" to -0026". Greatest breadth 

 of V. -0011". v.v. 



Bail. Mic. Org. fig. 38. Dorrjphora elegans, Roper, Mic. Journ. vol. ii. p. 284. 



Marine. In the mud of Pembroke Harbour, August 1854, Mr. Roper. 

 (New York, on Grinnellia Americana ; communicated by Br. Arnott. Near 

 Marseilles, May 1854, JF. Sm.) 



B. 



The following list includes those British forms described or figured 

 by other writers, which are either unknown to me, imperfectly known, 

 or appear to belong to species included in Vol. I. of the present 

 Work :— 



Epithemia gibberula, Ehr., Greg. Mic. Journ. vol. 2. pi. iv. 2. 



Eunotia incisa, Greg. Mic. Journ. vol. 2. pi. iv. 4. v.s. 



This appears to be a new species ; but, not having seen it in a fresh state, 

 I am unable with certainty to determine either its generic or specific characters. 

 It will probably be found to be a Himantidium. > Its valves are arcuate, 

 rounded or subacute at their extremities, with subterminal notches or depres- 

 sions on their concave margins ; striae 44 in *001". Length -0016" to '0022". 



Eunotia Falx, Greg. Mic. Trans, vol. ii. p. 105; Mic. Journ. vol. 3. 



pi. iv. l = Synedra Hemicyclus, Ehr. in Kiitz. Sp. Alg. p. 48. Ehr. 



Microg. pi. xvi. i. 38 & xvi. ii. 47- 

 Cymbella truncata, Greg. Mic. Journ. vol. 3. pi. iv. 3 = C. affinis, 



W. Sm. Synopsis, pi. xxx. 250. v.s. 



