490 Mr. J. Ralfs on the British species of Achnantlies. 



I have seen no specimen of tlie Achnanthes Carmichaelii of 

 Greville. 



1. A. longipes, Ag. Lateral surfaces turgid, appearing in the front 

 view, with evident transverse dotted strise, elliptic or elliptico- 

 lanceolate with the ends somewhat obtuse ; stipes longer than the 

 frustule. Ag. Consp. Diatom, p. 58 ; Grev. in Hook. Br. Fl. vol. ii. 

 p. 404 ; Harv. Br. Alg. p. 200 ; Ktz. Syn. Diatom, in Linnsea 1833, 

 p. 576 ; Ehr. Infus. p. 227. pi. 20. f. 1 ; Pritch. Infus. p. 232. Dia- 

 toma vexillum, Jurg. Dec. 6, no. 6 ! Conferva stipitata, Eng. Bot. 

 t. 2488 ! 



On the smaller marine algae. Southampton, Miss Hill; Torquay, 

 Mrs. Griffiths ; Shoreham, Mr. Borrer ; Newhaven, Mr. Jenner ; Pen- 

 zance, Ilfracombe. Aberdeen, Dr. Dickie ; Dublin Bay, Miss Ball 

 (according to a specimen from Mr. W. Thompson). 



It is distinctly visible to the naked eye, and forms on the in- 

 fected plant a fringe of a brown colour, which becomes whitish 

 when diied. 



Fronds aggregated, flag-like, consisting of a few (2 to 8) large 

 frustules on a stout stipes, which is from two to four times the 

 length of a frustule. The frustules are much bent in the middle ; 

 the central portion varies in breadth, but always appears hke a 

 band between the turgid lateral portions, and is separated from 

 them on each side by a pellucid line, within which is a longitu- 

 dinal series of short transverse strise. 



When the central portion is broad there are again other series 

 between these, but they are very faintly marked, and not percep- 

 tible except under the highest power of the microscope ; in fact, 

 under a low power the central portion exhibits no markings. 



The superior lateral portion is convex, and that of the terminal 

 frustule most so : the inferior lateral portion is concave in the 

 middle, and its ends are often slightly directed upwards : both 

 sm'faces have numerous strongly marked, dotted, transverse striae, 

 which are very conspicuous at the outline. 



The lateral view is elliptic or elliptico-lanceolate, sometimes 

 slightly constricted at the centre on one or both margins, some- 

 times nearly straight, but the ends are always somewhat obtuse. 



The colouring matter is either diffused or collected into a 

 roundish central spot. 



Plate XIV. fig. 7. Achnanthes lonc/ipes : a, central portion ; b, superior 

 lateral portion; c, inferior lateral poi-tion ; </, punctum. Fig. 8. Several 

 individuals : b, frustules deprived of their colouring matter ; c, superior 

 lateral view ; d, inferior lateral view. 



2. A. brevipes, Ag. Lateral surfaces turgid, appearing in the front 

 view, with transverse distinctly dotted striae ; stipes shorter than 

 the frustule ; lateral view lanceolate with subacute extremities. 

 Ag. Consp. Diatom, p. 59 ; Grev. Crypt. Fl. t. 295 ; Grev. in Hook. 

 Br. Fl. vol. ii. p. 404 ; Harv. Br. Alg. p. 199 ; Berk, in Eng. Bot. 



