90 BRITISH DIATOMACE.E. 



truncated extremities ; V. linear-acute ; striee obscure. Length of 

 frustule •0033" to -0058". v. v. 



Navicula curvula, Ehr. Inf. xiii. 14 ? Kiitz. Bacill. iv. 31 1 Nitzschia Sigma- 

 tella, Greg. Mic. Journ. vol. 3. pi. iv. 2. 



Fresh water. Poole Bay, Sept. 1854 ; New Forest, Hampshire, Sept. 1854; 

 Lough Avaul, Co. Cork, June 1855, W. Sm. Elchies, Bamffshire, Aug. 1854, 

 Dr. Gregory. 



Almost identical in form with N. Sigma, but distinguished from that species 

 by its far more delicate striae and freshwater habitat. 



32. Amphiprora elegans, n. sp. F. straight; F. V. lanceolate, con- 

 striction very slight; V. lanceolate; striae 40 in *00l". Length of 

 frustule -0088" to '0124". v.v. 



Marine. Harwich, July 1853, Mr. Bleakeley. Milford Haven, March 



1854, Mr. Roper. Salt Pans, Hampshire, Sept. 1854 ; Cork Harbour, June 



1855, &c, W.Sm. 



Distinguished from A. vitrea by its longer and, comparatively, more lanceo- 

 late and slender frustule and closer striae. 



33. Amphipleura infiexa. Breb. Frustule arcuate, linear, slightly 

 attenuated towards the rounded extremities ; striae 52 in '00 1". v.s. 



Breb. in Kiitz. Sp. Alg. p. 88. ad specimina authentica quae misit cl. collector. 



Marine. Ilfracombe, Mr. Ralfs ; communicated by M. Be Brebisson. 

 (Coast of Normandy, M. Be Brebisson.) 



34. Navicula rhomboides, Ehr. 



Var. /3. V. elliptical-lanceolate ; extremities rounded, v.v. 



Freshwater: frequent with Var. a. New Forest, Hampshire, Sept. 1854, 

 W. Sm. Near Lancaster, Aug. 1853, Mr. Johnson. Ben Lomond, Sept. 

 1854, Dr. Arnott. Elchies, Bamffshire, Aug. 1854, Dr. Gregory. 



35. Navicula firma, Kiitz. 



Var. y. Extremities cuneate. v.s. 



Navicula amphigomphus, Ehr. in Kiitz. Bacill. xxviii. 40. et Nav. microstoma, 

 Kiitz. Sp. Alg. p. 71. ad specim. quae misit am. De Bre'bisson. 



Fresh water. Lough Leven, Aug. 1854, Dr. Gregory. 



The semblance of a marginal band in this, and some allied forms, appears 

 to arise from the bending inwards of the edges of the valves towards the line 

 of suture. 



