234 DESCRIPTION OF [Polyyasliica, 



from three to seven internal longitudinal lines, transversely 

 striated. The clusters of banners form curved ribbons ; 

 ova greenish -yellow, at first, but becomes reddish or violet. 

 Fig. 203 represents two-and-a-half tablets, with dispersed 

 ova, and fig. 204 an old one, with them united ; they are 

 both attached to sea- weed (Callithamnium). Length of 

 single lorica l-570th to l-200th. 



Section IV. — Lorica Invested or Double. — 

 Lacernata. 



Genus LXXIIL Frustulia. The gelatinous little ship 

 Animalcules are characterized by a double envelope, the 

 siliceous lorica being enveloped in, and scattered or 

 grouped together among, an indefinitely-formed gelatinous 

 mantle, or lacerna. The true lorica has six openings, two 

 at each end, and two in the middle. The ova cluster is 

 divided into from two to four leaf-like portions ; digestive 

 cells and bright glandular organs are often visible. They 

 are closely allied to Navicula. No figure of this genus is 

 given in Die Infusionsthierchen. 



342. Frustulia appendiculata (Cymbella, Ag.) The 

 brownish Frustulia. — Lorica straight, lanceolate, and 

 smooth (?) ends obtuse ; they are scattered through an 

 amorphous gelatine. This species is like Navicula gracilis, 

 but rounded upon the dorsal and ventral surfaces, and 

 more parallel on the lateral ones. The central opening is 

 broad transversely ; the end ones are round. Ehrenberg 

 has often observed self-division. Found upon the damp 

 walls of the mineral springs of Carlsbad. Length l-8000th 

 to 1-1 150th. 



