BRITISH DESMIDIE.E. 149 



* Empty frond either striate or granulate, generally reddish. 



I . P. margaritaceum (Ehr.) ; frond cylindrical with rotundato-trun- 

 cate ends ; pearly granules in longitudinal series. 



a. Frond fusiform^ constricted at the middle ; granules distinct, 



giving a denticulate appearance to the margin. 

 /3, Frond linear, scarcely constricted at the middle; granules 

 giving a denticulate appearance to the margin, somewhat 

 scattered near the suture. 

 y. punctatum ; frond linear, neither constricted at the suture nor 

 denticulate at the margin ; granules appearing like puncta. 



Closterimn maryaritaceum, Ehrenberg, Infus. p. 95. t. 6. f. 13 (1838). Me- 

 neghini, Synop. Desmid. p. 236. Jenner, Fl. of Tunhridye Wells, p. 196. 

 Kiitziug, Phy. Germ. p. 132. Hassall, Brit. Freshwater Alyce, p. 376. 



Penium maryaritaceum, Brebisson, in lit. (1846). 



a. Ashdown Forest, Sussex, Mr. Jenner. Penzance, J. JR. 



/3. Near Bristol, 3Ir. Thwaites. Warbleton, Sussex, Mr. Jenner. 



y. Dolgelley, J. R. Ashdown Forest, and Henfield, Sussex ; and Reigate, 

 Surrey, Mr. Jenner. Near Aberdeen, Dr. Dickie and Mr. P. Grant. Am- 

 bleside, Mr. Sidebotham. 



Berlin, Ehrenhery. Falaise, Brebisson. 



Frond minute, six to twelve times longer than broad, rough with pearly 

 granules which are arranged in longitudinal rows. The forms which I have 

 here considered varieties diifer so much, that it is probable they will prove to 

 be distinct species. It will be seen that the variety /3. is intermediate between 

 the extreme states, and since neither of our British forms agrees with Ehren- 

 berg's figure and description, I shall describe each in detail. 



a. Frond stout, rounded at the end, distinctly constricted at the middle ; 

 fillets distinct, interrupted and, as well as the endochrone, divided into four 

 equal portions by three pale transverse bands. Near each extremity there is 

 an obscure globule ; segments somewhat fusiform. The empty frond is nearly 

 colourless, and the pearly granules are distinct and give a denticulate appear- 

 ance to the margin. Besides the middle transverse suture, there are two others 

 corresponding with the interruptions of the endochrome. I have received this 

 form from M. de Brebisson as his Penium maryaritaceum. It differs from 

 Ehrenberg' s figure of Closterium maryaritaceum in being broader, more con- 

 stricted at the middle, and having more ventricose segments. The arrange- 

 ment of the endochrome and the position of the globules also differ. 



The variety /3. agrees in colour -with the preceding, but it is shorter, and its 

 sides are parallel. The granules are distinct, but less regular. I have only 

 seen it after the endochrome had collapsed. 



The variety y. is elongated, slender, linear, truncate at the ends, and scarcely 

 constricted at the middle. The endochrome is divided into four portions by 

 transverse pale bands ; but there are no fillets or globules with moving par- 

 ticles. The empty frond is reddish, especially at its extremities, the last- 

 formed segment being generally paler than the other. The pearly granules 



L 2 



