44 BRITISH DIATOMACEyi:. 



owing to their deeper constriction, the central position of their keel, 

 and their less firmly siliceous structure. They are frequently found 

 in large numbers, and M'ith the exception of one species are marine in 

 their habitat. They are common in the estuaries of all our larger 

 rivers, and the sheltered bays of the southern and western coasts of 

 England. I have also examined specimens from the coast of Nor- 

 mandy, the shores of the United States, and the Arctic Regions. 



1. Amphiprora alata, Kiiiz. F. twisted; F. V. elliptical, with 

 rounded extremities ; V. linear-eUiptical ; keel accompanied by a 

 double line of puncta ; surface of V. striated; striae 42 in -001". 

 Length -0025" to -0052". v.v. 



Kiitz. Bacill. iii. G3. Bright. Inf. x. 1.3. Prit. Anim. xvi. 5 & 7. Bail. 

 Obs. 8, 9, 10. 



Mariae and brackish water : very common. Coast of Sussex, April and 

 Aug. 1850, W. Sm. 



Plate XV. 124. Frustule with endochrome. Frontispiece, fig. CXXIV. 



2. Amphiprora paludosa, n. sp. F. twisted ; F. V. elliptical, with 

 round or truncate extremities ; constriction very deep ; V. striated ; 

 strise 60 in -001". Length -0016" to -0042". v.v. 



In fresh or shghtly brackish water. Near Lewes, Sept. 1852, W. Sm. 

 Supp. Plate XXXI. 269. 



3. Amphiprora didyma, n. sp. F. straight, elliptical, deeply con- 

 stricted ; striae faint, 7^ in -001". v.v. 



Marine. Lytham, Lancashire, Sept. 1849, JF. Sm. 

 Plate XV. 125. 



4. Amphiprora vitrea, n. sp. F. straight; F. V. elliptical, con- 

 striction very slight; V. lanceolate, striated; striae 52 in "OOl". 

 Length -0023" to '0052". v.v. 



Marine. Shoreham Harbour, Sept. 1852, W. Sm. 

 Supp. Plate XXXI. 270. 



5. Amphiprora constricta, Ehr. F. membranaceous, hyaline, 

 straight, elliptical ; V. linear-elliptical, with a central sinus and 



