ANIMAL NATURE OF DIATOMEiE. 413 



{curvatiim) they are curved. The secondary are obovato- 

 acute in the first eleven species; elliptico-lanceolate in four, 

 {dichotomum, qfflne, intricatum, lanceolatum ;) in all the rest 

 they are distinctly capitate or more or less panduriform. 



30. Sphenosira. — Individua in filum complanatum 

 anceps rectum arete conjuncta, a latere secundaria apicibus 

 incequalibus ; apertwra media distincta. 



Kiitzing himself observes, that the single species of 

 this genus {8. catena) belongs rather to the genus 

 Diadesmis of the following family, because, although the 

 apices of the secondary surfaces are unequal, it w^ants the 

 constant character of all Gomphonemese, the cuneiform 

 primary surfaces ; whilst we see represented the associated 

 form of Sphenella angustata. 



The Gomphonemese, according to Kiitzing, {Sphenella, 

 Gomphonema, Sphenosira,) are related to the Licmo- 

 phorese in form and development. They differ by the 

 absence of the vittse, and the presence of a central per- 

 foration in the lateral surfaces. The internal substance 

 is disposed in two laminae extended over the primary 

 surfaces ; in opposition, therefore, to what takes place in 

 the preceding family of Cymbellese. Ehrenberg notices, 

 also, colourless vesicular spaces. We must not omit, 

 that even in Gomphonemese the primary surfaces are 

 traversed by the usual two longitudinal striae, terminating, 

 superiorly at least, in distinct apertures. 



31. Navicula. — Individua singularia libera, regu- 

 laria, rectangula, prismatica ; apertura media rotunda. 



In this genus, the richest of all in species, and the 

 type of a family the richest of all in genera, from which 

 some have adopted the name Naviculese rather than that 

 of Diatomese for the entire class, the constant character 

 is the symmetry of each pair of surfaces as well as of both 

 extremities. We have seen this character, with a few 

 exceptions, in the family of Fragillariese, and still more 

 in the Surirellese. Hence it follows, that in some genera 



