456 Mr. J. Ralfs on the DiatomaceEe. 



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

 Landsboroiigh. Ireland, Mr. D. Moore and Mr. IV. 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 strise, which are fainter towards the ends of the fi'us- 

 tules. 



The lateral surfaces are linear-elliptic with close transverse 

 striae, and are divided by a line passing do^Ti the centre, a small 

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

 times forms a central spot. 



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

 which has severallongitudinal strise. Ag. Consp. Diatom, p. 61 ; 

 Harv. Br. Alg. p. 199. Achnanthcs vnipunctata, 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 algae : autumn. Ireland, Mr. D. Moore. Torquay, 



M)-s. Griffiths ; Little Hampton, Mr. Borrer ; Penzance. 



Filaments minute, pale yellowish bro^ra, 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 striae, one 

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

 more strongly marked and its striae 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 stri?e are arranged in a curve. En- 

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

 colom'. Lateral surfaces lanceolate, without stris. 



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

 have received from Mrs. Griffiths some interesting varieties of 

 that plant. In some spechnens longitudinal series of transverse 

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

 tules. Mixed ^\^th this variety I fomid another, in which the lon- 

 gitudinal striae, 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 StriateUa, it should be removed to that genus ; and as all the 

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

 which has a prior claim, might be conveniently restored. 



