476 ANIMAL NATURE OF DIATOME^!. 



general from the other law (which is laid down as general), 

 that the direction of the vittse is always longitudinal. In 

 either case, the genus Terpsinoe varies entirely from its 

 allies, so that I think it must be regarded as the type of 

 a distinct family. 



Owing to the mere presence of vittse, Kiitzing has 

 elevated the group of three families just examined, no less 

 than to a degree superior to that of an order, and which 

 he denominates a tribe. The analysis we have instituted 

 appears to me sufficient to prove that this characteristic 

 condition is solely due to the larger development of an 

 organ which really exists, or is in some degree repre- 

 sented, in the various families of the preceding tribe. 

 And though, systematically, we might wish to assign it a 

 great importance, yet in a natural classification it must 

 certainly be subordinate to the assemblage of characters. 

 Therefore, abstracting this character, and looking solely 

 to natural affinities, I believe that the Licmophorese ought 

 to be placed near the Gomphonemese, with the exception 

 that the genus Licmophora is to be placed by the side of 

 Synedra, and therefore in the family of Surirellea? ; and 

 all the other vittated Diatonieae must be ranged in the 

 order Fragillarieae. 



58. COSCINODISCUS. Individua solitaria, lidera, lorica 

 bivahis silicea, in latere secundario disciformis, cribrata. 



The only essential character that distinguishes this 

 genus from the Cyclotella, is the areolation of the 

 secondary surfaces. And it is entirely on this account, 

 that, whilst belonging to the first tribe, it is placed in the 

 last. We ought to repeat here, that when treating of 

 Cyclotella, we noticed the points and radiated lines in 

 the lateral surfaces of the freshwater species (operculata, 

 Meneghiniand} and the fossil ones, (minutula, Rotula,) a 

 circumstance that imperiously requires an union of the 

 two genera. In what relates to this areolation, the expres- 

 sion cribrata, of Kiitzing, includes a false idea, inasmuch 

 as these cells are not perforations at all, as this author 



