Mr. J. Ralfs on the British species of Achnanthes. 491 



t. 2842. f. 1 ; Ktz. Synop. Diatom, p. 574 ; Ehr. Tnfus. p. 227. 

 pi. 20. f. 2 ; Pritch. Infus. p. 232. f. 199—202. Echinella stipitata, 

 Jurg. Dec. 13, no. 8! 



On marine algse. Southampton, Miss Hill; near Shoreham, Sus- 

 sex, Mr. Jenner. 



This species bears a considerable resemblance to Achnanthes 

 longipes. Like that species_, its frustule is strongly bent, and its 

 central portion, which is marked by longitudinal series of shoii; 

 transverse strise, appears like a band between the turgid lateral 

 portions. These too are similar in shape to those of Achnanthes 

 longipes, and are marked in like manner with transverse dotted 

 striae, which are interrupted by a longitudinal pellucid line pass- 

 ing down the middle. Notwithstanding these similarities it may 

 at first sight be distinguished from Achnanthes longipes, as its 

 stipes is very sbort ; its lateral view is more acute, and often 

 rather suddenly attenuated at the ends, and its transverse striae 

 are more distinctly dotted ; indeed, in the more elongated frustules 

 are series of short lines, and in its central portion the longitu- 

 dinal series of striae are also much more distinct. 



The lateral view is more frequently constricted in the centre 

 than in Ach. longipes. 



The frustules are three to six times longer than broad. 



I have not seen this species in a recent state : when dry it is 

 of a whitish colour; and under the microscope the colouring mat- 

 ter is either scattered or collected into a central spot. 



Plate XIV. fig. 9. Achnanthes brevipes: b, frustules deprived of their 

 colouring matter ; c, superior lateral view ; d, inferior lateral view. 



3. A. subsessilis, Ktz. Lateral surfaces elliptic, obtuse, striated; 



stipes shorter than the frustule. Ktz. Syn. Diatom, in Linnaea 



1833, p. 576 ; Ktz. Alg. no. 42 ! ; Ehr. Infus. p. 228. pi. 20. f. 3 ; 



Pritch. Infus. p. 233. 



On Conferva tortuosa and filiform species of Enteromorpha, chiefly 

 in salt-water marshes. Hayle near Penzance, near Holyhead, by the 

 Menai Bridge, and Penman Pool near Dolgelley. 



It is very minute, scattered, not visible to the naked eye ) but 

 wben plentiful gives a brown tinge to the plant on which it grows. 



Frustules generally one or two (seldom more than three) on the 

 stipes, slightly bent, two or three times as long as broad ; lateral 

 surfaces elliptic, striated, slightly tm*gid, with obtuse ends : both 

 surfaces have a longitudinal pellucid line, and the inferior a trans- 

 verse one also. In the front view the upper margin is slightly 

 convex, and the lower one concave with a distinct punctum ; the 

 ends of the lateral strise, which are much less strongly marked 

 than in the preceding species, appear along the margin, but the 

 lateral portions are scarcely seen. The central portion is either 

 without markings or has very obscure longitudinal series of short 



3K2 



