404 ANIMAL NATURE OF DlATOME^l. 



of the last two sections, (oblonffte, ovatce, elliptic^,} and 

 in the sub-genus Podocystis, still remain very evident, 

 viz., the terminal surfaces. Kiitzing observes, that in 

 conformity with the flattened form of the SurireUa, and 

 the lengthened form of the Synedrte, the intermediate 

 spaces are placed laterally on the median line of the first, 

 and are accumulated at the extremities of the second. 

 But this accumulation never occurs until after death. 

 Whilst they are alive the internal colouring substance is 

 mostly situated along the median line of the lateral sur- 

 faces, or sometimes along the sides of these, and then in 

 four to eight distinct lobes. In some species it is dis- 

 posed in symmetrical and equidistant transverse fasciae. In 

 the central region there is often a transparent space, and 

 many other varieties are met with ; these are quite suf- 

 ficient to indicate a complicated organisation, but we do 

 not know how to interpret them rightly. Finally, we 

 ought not to pass over in silence the important organic 

 condition of two very distinct longitudinal lines on each 

 of the primary surfaces, terminated at both extremities in 

 minute perforations; a condition clearly delineated by 

 Kiitzing in seventeen species, and which, in the smaller 

 ones, we may suppose to have been obscure, or even 

 unobserved. 



Comparing together the four genera (Campylodiscus, 

 Suriretta, Bacillaria, Synedra,} which constitute the 

 family of Surirelleae, it is easily perceived that the last 

 two only deviate from the Fragillarieae by the character of 

 interrupted striae ; and the first two deviating sensibly in 

 the succession of species from the circular shape of the 

 lateral surfaces, or of the transverse section, establish a 

 transition between the Melosirea3, and the group formed 

 of these two genera, along with the Fragillarieae and the 

 Meridieae. Hence it is impossible to establish an organ o- 

 graphical character that shall embrace the entire family 

 and strictly represent its type. For even restricting the 

 organographical data we possess to the predominance of 

 the vertical surfaces (primary and secondary), with the 



