456 Mr. J. Ralfs on the Diatomacea?. 



On marine algse : not uncommon. Ardrossan, Ayrshire, Rev. D. 

 Landsborough. Ireland, Mr. D. Moore and Mr. W. Thompson. Devon- 

 shire, Mrs. Griffiths ; Sussex, Mr. Jenner ; Aberystwith, Penzance. 



Filaments, when recent of a dark olive-brown, become greener 

 in drying ; they are rigid, thick, elongated, very fragile, and do 

 not adhere to paper ; the frustules irregularly separate, and co- 

 here by their angles. Stipes very short and thick. 



Frustules vary from nearly equal in length and breadth to twice 

 as broad as long, with numerous longitudinal series of short 

 transverse stria?, which are fainter towards the ends of the frus- 

 tules. 



The lateral surfaces are linear-elliptic with close transverse 

 striae, and are divided by a line passing down the centre, a small 

 space at each end being destitute of stria?. The endochrome some- 

 times forms a central spot. 



2. S. unipunctata, Ag. Stipes slender, much longer than the frustule, 

 which has several longitudinal striae. Ag. Consp. Diatom, p. 61 ; 

 Harv. Br. Alg. p. 199. Achnanthes unipunctata, Grev. Cryp. Fl. 

 t. 287 ; Kutz. Syn. Diatom, in Linnsea 1833, p. 573. Diatoma 

 unipunctatum, Ag. Syst. Alg. p. 6; Grev. in Br. Fl. vol. ii. p. 405. 

 On marine algse : autumn. Ireland, Mr. D. Moore. Torquay, 



Mrs. Griffiths ; Little Hampton, Mr. Borrer ; Penzance. 



Filaments minute, pale yellowish brown, consisting of but few 

 frustules, which cohere at the alternate angles. Stipes slender, 

 long ; frustules generally rather longer than broad ; the angles 

 slightly truncated, with two series of longitudinal stria?, one 

 series occupying the middle and the other the ends ; the latter is 

 more strongly marked and its stria? are of different lengths, 

 longer in the centre and shorter towards the lateral margins of the 

 frustule, and all are terminated by puncta, which in consequence 

 of the different lengths of the stria? are arranged in a curve. En- 

 dochrome pale, generally collected into a central spot of a deeper 

 colour. Lateral surfaces lanceolate, without stria?. 



P.S. Since my description of Diatoma marinum was written, I 

 have received from Mrs. Griffiths some interesting varieties of 

 that plant. In some specimens longitudinal series of transverse 

 stria? were more or less evident on the central portion of the frus- 

 tules. Mixed with this variety I found another, in which the lon- 

 gitudinal stria?, extending from the ends towards the middle, are 

 serpentine. 



I find this species generally attached at the angle of the basal 

 frustule by a short stipes. As therefore it differs in no respect 

 from Striatella, it should be removed to that genus ; and as all the 

 species of Striatella are marine, its old specific name teniceformis, 

 which has a prior claim, might be conveniently restored. 



