BRITISH DIATOMACEiE. 91 



36. Navicula pygmaea, Kiitz. V. elliptical-oblong, subacute. Length 

 •0012". Breadth of V. -0005". v.v. 



Kiitz. Sp. Alg. p. 77. ad specim. quae dedit cl. De Brebisson. 



Brackish water. Itford, Sussex, Nov. 1853 ; Cork Harbour, Nov. 1855, 

 W. Sm. Coast of Norfolk, Mr. Bleakeley and Mr. Bridgman. 



Differs from N. minutula, Synop. vol. i. xxxi. 274, only in the greater com- 

 parative length and subacuteness of valve : that species must therefore yield 

 place to the present, and be described in future as N. pygmoea var. /3. 



37. Navicula Scutelloid.es, W. Sm. Valve nearly orbicular ; striae 

 moniliform, 18 in -001". Length of F. -0007". Breadth of V. 

 •0006". v.v. 



W. Sm. in Greg. Mic. Journ. vol. iv. p. 4. pi. i. 15. 



Fresh water. Ormesby, Norfolk, Sept. 1853, Mr. Bridgman. Rosthern 

 Mere, Cheshire, Sept. 1855, Dr. Arnott. Cantyre Peat, &c. 



38. Navicula Bacillum, Ehr. V. linear, extremities rounded ; stria? 

 54 in -001". Length of F. -001 1" to -0022". Breadth of V. 

 •0005". v.s. 



Ehr. in Kiitz. Bacill. xxviii. 69. ad specim. authen. quae dedit am. De Bre'bis- 

 son. Nav. bacillaris, Greg. Mic. Journ. vol. 4. pi. i. 24. 



Fresh water. Dundee, Dec. 1855, Dr. Gregory. 



39. Navicula laevissima, Kiitz. V. linear, or slightly inflated at 

 centre ; extremities truncate ; striae 48 in *00l". Length of valve 

 •0008" to -0019". Breadth of valve -00025" to -0005". v.v. 



Kiitz. Bacill. xxi. 14. Stauroneis rectangidaris, Greg. Mic. Journ. vol. 2. 

 pi. iv. 17. 



Freshwater: frequent. Lewes, March 1853 and April 1854; Glengariff, 

 Co. Cork, June 1855, &c, W. Sm. Lough End near Edinburgh, March 

 1854, Dr. Gregory. Bridge of Allan, Dr. Arnott. Ulverstone, Dec. 1854, 

 Miss Hodgson. 



There is no true stauros in this species : a sufficient defining power with 

 accurate illumination shows that the striae extend over the entire surface of 

 the valve not occupied by the nodules and median line. 



40. Navicula pectinalis, Breb. F.V. extremities truncate; V. linear- 



