BRITISH DIATOMACEiE. 31 



Length of frustule -0004" to -0008". Breadth of valve -0002" to 

 •0003". v.v. 



Bre'b. in Kutz. Sp. Alg. p. 54. ad specim. authen. quae communicavit cl. 

 inventor. 



Fresh water : very generally distributed in subalpine districts. Beachey 

 Head, Sussex, Aug. 1851. Portisham Spring, Dorsetshire, Sept. 1854. 

 Moanarone, Co. Cork, Aug. 1855, &c, W. Sm. Aberdeenshire, Dr. Dickie. 

 Ayrshire, Dr. Landsborouyh. Kendal, and Ulverstone, March 1854, Miss 

 E. Hodgson. Cumbrae, May 1854, Mr. Hennedy. (Puy de Dome, elev. 3000 

 feet, June 1854, W. Sm. Falaise, M. De Brebisson.) 



Plate XXXVII. 304. 



2. Achnanthidium coarctatum, Breb. Filament of few frustules, 

 2 to 6 ; valves elliptical, with a central constriction and slightly 

 attenuate ends, striated ; upper with a median line and distinct 

 stauros ; under with median line only ; striae 40 in *00l". Length 

 of frustule -0005" to '001 5". v.v. 



Bre'b. in lit. cum specim. authen. Jan. 1852. W. Sm. Ann. ser. 2. vol. 15. 

 pi. i. 10. Stauroneis constricta, Ehr. in Kiitz. Bacill. xxix. 19? 



Fresh water. Grassmere, Aug. 1853, W. Sm. Cramond near Edinburgh, 

 Oct. 1855, Dr. Arnott. Haverfordwest, April 1855, Mr. Okeden. (Basaltic 

 Cave at Royat, in the Auvergne, June 1854, W. Sm.) 



Supp. Plate LXI. 379. 



3. Achnanthidium microcephalum, Kiitz. Filament of 2 or 4 

 frustules ; valves elliptical-lanceolate, constricted towards the ex- 

 tremities, with a median line, and central and terminal nodules; 

 striae obscure. Length of frustule "0004" to *0006". v.v. 



Kiitz. Bacill. Hi. 13 & 21 ; Sp. Alg. p. 54. ad specim. authen. quae misit cl. 

 De Bre'bisson. 



Fresh water. Aberdeenshire, Dr. Dickie. (Falaise, M. De Brebisson.) 



I place this form doubtfully in the present genus, for not only are the 

 valves apparently symmetrical, but the geniculate character of the frustule is 

 often absent : the minuteness of the species precludes any very certain dia- 

 gnosis, and I yield to the authority of M. De Brebisson, with whose specimens 

 Dr. Dickie's very accurately agree. 



Supp. Plate LXI. 380. 



4. Achnanthidium lineare, W. Sm. Filament of 2 to 4 frustules ; 

 valves linear, rounded ; upper with median line only ; lower with 



