BRITISH DIATOMACE.E. 81 



3. Homceocladia sigmoidea, n. sp. Frond linear, simple; frus- 

 tules irregularly fasciculated in bundles of about six ; F. V. sigmoid ; 

 V. linear, attenuated towards the extremities. Height of frond 

 •3" to -6". Length of frustule -0025". Breadth of valve -0002". v.v. 



Brackish water: attached to grass. Near Wareham, Dorset, Jan. 1 850, W. Sm. 

 Plate LV. 349. 



Suppl. Genus 58. ASTERIONELLA, Hass. 



Frustules linear, inflated towards one or both extremities ; adhering 

 by their adjacent angles into a star-like filament. 



The present genus, first constituted by Mr. Hassall in his pamphlet 

 " Microscopic Examination of the Water supplied to the Inhabitants 

 of London," was not known to me when I arranged the genera of the 

 present work. It ought probably to be placed next after Diatoma, 

 as it agrees with that genus in the general form of its frustules, differ- 

 ing from it chiefly in the mode of adherence which takes place after 

 self-division. 



The species which have reached me through the kindness of the 

 correspondents mentioned below were none of them in a satisfactory 

 condition for examination, and it would require a further acquaint- 

 ance with them in a fresh state to clear up several points in their 

 habit and structure. 



1. Asterionella formosa, Hass. Star of from four to eight frus- 

 tules ; on F. V. somewhat more enlarged at the base (point of 

 adherence) than at the summit. Length of frustule *002l" to 

 •0031". v.s. 



Hass. I. c. p. 10, &c. 



Fresh water: in water supplied to the town of Tenby, March 1853, Mr. 

 Roper. Rosthern Mere, Cheshire, Sept. 1855, Dr. Arnott. 



2. Asterionella Ralfsii, W. Sm. Frustules on F. V. exactly linear ; 

 valve attenuated towards one extremity, constricted towards the 

 other, which is rounded and capitate ; striae obscure. Length of 

 frustule -0018". v.s. 



Diatoma stellare, Ralfs, MSS. ad specim. in Herb. Jenn. 



VOL. II. G 



