414 DIATOM ACE^J. 



verified my observation on these minute striae : when first I 

 observed them, I thought that they were found only in the 

 undulated variety of the plant, and that this therefore might 

 form a distinct species. I am now satisfied, however, that the 

 striae are to be found in every well-developed specimen ; and 

 the difference observed in the end view of the frustules in 

 certain species is indicative of merely a condition of the 

 plant. 



A remarkable state of this species has been met with by 

 Mr. Ralfs and Mr. Jenner. In this, within each frustule is 

 enclosed apparently a second frustule of a more or less oval 

 form, and striated laterally in the same way as the extremities 

 of the cells. 



Occasionally it happens in this and in other species and 

 genera of Diatomacece that the cells in their front aspect 

 are not in the form of a parallelogram, but somewhat cuneate : 

 this occurs in consequence of the frustule being divided ob- 

 liquely, and not by a straight line. 



The frustules, Mr. Ralfs observes, have sometimes a central 

 pellucid spot, which does not appear to be connected with the 

 endochrome. 



When recent, Fragilaria pectinalis is of a dark brown, but 

 in drying it turns to a greyish green, with a metallic lustre. 



2. FBAGILAEIA HYEMALIS Lyngb. 

 Plate XCV. Fig. 5. 



Char. Filaments very fragile. Frustules long. Sides slightly 

 emarginate, puncta very small. End view elliptico-lanceo- 

 late, with from two to seven or eight well-marked stria, 

 which terminate in distinct puncta along the anterior ter- 

 minal margins of the frustules. 



Lyngb. t. 63. ; Ag. Syst. p. 7. ; Consp. Diatom, p. 63. ; 

 Kiitz. in Linnaea, 1833, p. 72. Fragilaria confervoides 

 Grev., in Br. Flor. vol. ii. p. 403. ? Harv. Br. Algje, 

 p. 197. ; Ralfs, in Annals, vol. xii. pi. ii. f. 3. 



Fragilaria turgida Ehr., Infus. pi. xv. f. 13. 



