ANIMAL NATURE OP DIATOMEjE. 403 



****** Bimaria ; bacillis in tabulam connatis, demum 

 modo Diatomatis disruptis et angulis alternis cohcerentibus. 



Besides the sectional character which intimates an 

 analogy with Biatoma, the only species that figures here 

 {8. rumpens) differs from all the other Synedros by the 

 tumid and rounded extremities of the primary surfaces. 



From this rapid examination of the sections into which 

 the seventy species of Synedrce are divided, and to which 

 Kiitzing adds seven more as uncertain, it appears that 

 very different relations might be established among them; 

 and that if in the greater portion an evident similitude 

 in form would seem to indicate a very distinct genus, in 

 many there appear indications of resemblance to genera 

 and famihes totally different. We must therefore repeat, 

 in this instance, that in the want of data whereby to 

 judge of the organic importance of character, and in 

 the arbitrary nature of the selection, of necessity resulting, 

 Kiitzing has achieved a supremely laborious and diligent 

 task, by discriminating, describing, figuring with won- 

 derful accuracy, and distributing with some sort {qua- 

 cunque) of systematic order so immense a number of 

 species. As to the organ ographical considerations which 

 can be instituted in this genus, they reduce themselves 

 to the single one of length predominating over breadth, 

 and the eminently bacillary form derived from it. Thus 

 Kiitzing observed the opposite characters o^ Synedrce and 

 Surirellce ; that the lateral surfaces exceeded in one, the 

 primary surfaces again in the other. But it is not in this 

 that the opposition really exists. For even among the 

 Surirellcs we have some {medio plerumque constrictce) of 

 those which do not exhibit the boasted prevalence of the 

 lateral surfaces, and which, therefore, we might with 

 equal propriety enumerate among the Synedrm ; whilst 

 almost all Synedree of the first section {Scaphularid), and 

 some of the second {Echinaria) want even the last dis- 

 tinctive character that would remain, — of being affixed. 

 The surfaces, which in all Synedree are really reduced to 

 the smallest dimensions, are the two which in Surirellae 



