398 DESCRIPTION OF [Pulj/jasfrica. 



Kiitzing would appear, indeed, to assign a higher importance to 

 the presence or absence of an umbilicus than ercn Ehrcnberg, for he 

 has constituted Sun'rella, with some other genera, into a family 

 Surirellcce, totally distinct from the family Kaviculece ; in fact, Suri' 

 rella and Kavicula belong to two different orders ; the former, 

 devoid of an umbilicus, to tho AstomaticecB ; the latter, j)0ssessing an 

 umbilicus, to the Stomaticce. 



According, therefore, to the foregoing opinions, Kiitzing retains 

 the transversely striated and umbilicated Pinnidaria with the smooth, 

 umbilicated Kavicula; as likewise the smooth Stauroneis with the 

 striated Stauroptera. 



A still more remarkable plan, pui'sued by the author just named, 

 is, the including in his family Kaviculeai those peculiar organisms, 

 having the outward general figure of minute, branched, or tufted 

 Algse, but intimately composed of innumerable, mostly minute, 

 na\dcula-likc bodies, enveloped in a gelatinous investment or thallus 

 and which Ehrenberg described as Bacillaria with a double lorica. 

 With these compound organisms, indeed, a relation is sometimes dis- 

 played by species of free Navicula, which are suiTounded by more 

 or less mucus ; but the first-named beings seem to form a more 

 natural group by themselves. To ti;ace an analogy, they bear the 

 same relation to the free, isolated Navicula, as do the polj^paries of 

 coral, or other aggi'cgatcd polypes, to the simple polj-pes ha-ving an 

 individual or isolated existence. 



This point is partly conceded by Kiitzing, who divides his family 

 Navicula into two sections : — .\'iz. (a.) True Naviculem, and fb.J 

 ScJdzonemc(S. In the first section he locates the following genera : — 

 viz., Navicula, Amjilnpleura, Ceratoneis, Stauroneis, Amjyhiprora, 

 A/tiphora, and Diadesmis ; in the second, Frustulia, Berkeleya, 

 Ehaphidof/loea, Homoeocladia, Scldzonema, Microniega, and Diclcieia. 



Surirella, as before remarked, gives name to a distinct family in 

 the system of Kiitzing — Surirellcce; which, in addition to that genus, 

 compreliends Camptjlodiscus, Bacillaria , and Synedra. 



On the sub- division and structural peculiarities of this great genus 

 Navicula, the Eev. W. Smith, in a recent paper (Ann. Nat. Hist 

 Jan. 1852), has the ensuing remarks : — 



'* I ghall restore the genus rinnularia of Ehrenberg, rejected by 



