292 



DIATOM ACE.E. FAMILY MERIDIEM. 



1 'are literally covered in the first warm clays of spring with a fer- 

 ruginous-coloured mucous matter, about a quarter of an inch thick, 

 which, on examination by the microscope, proves to be filled with 

 millions and millions of these exquisitely-beautiful siliceous bodies. 

 Every submerged stone, twig, and spear of grass is enveloped by 

 them ; and the waving plume-like appearance of a filamentous 

 body covered in this way is often very elegant." The frustules of 

 Meridiem are attached when young to a gelatinous cushion ; 

 but this disappears with the advance of age. — In the family 

 Licmophorece also the frustules are wedge-shaped ; in some genera 



Fig. 127. 



Fig. 128. 



Fig. 127.— Diaioraa vulgare:—a, side view of f rustule ; b, frus- 

 tule undergoing self- division. 



Fig. 128. — Grammatophora serpentina :— a, front and side views 

 of single frustule ; b, b, front and end views of divided frustule ■ 

 c, a frustule about to undergo self -division ; d, a frustule com- 

 pletely divided. 



they have transverse markings, whilst in others these are deficient ; 

 but in most_ instances there are to be observed two longitudinal 

 suture-like lines on each valve (which have received the special 

 designation of vittce) connecting the puncta at their two extremities. 



