ANIMAL NATURE OF DTATOME.E. 413 



(curvatum) they are curved. The secondary are obovato- 

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

 (dichotomum, affine, intricatum, lanceolatum ;} in all the rest 

 they are distinctly capitate or more or less panduriform. 



30. SPHENOSIRA. Individua in Jilum complanatum 

 anceps rectum arete conjuncta, a latere secundario apicibus 

 inaequalibus ; apertura media distincta. 



Kutzing himself observes, that the single species of 

 this genus (S. catena) belongs rather to the genus 

 Diadesmis of the following family, because, although the 

 apices of the secondary surfaces are unequal, it wants the 

 constant character of all GomphonemeaB, the cuneiform 

 primary surfaces ; whilst we see represented the associated 

 form of Splienella angustata. 



The Gomphonemeae, according to Kiitzing, (Sphenella, 

 Gomphonema, Sphenosira,} are related to the Licmo- 

 phoreae in form and development. They differ by the 

 absence of the vittae, 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 Cymbelleae. Ehrenberg notices, 

 also, colourless vesicular spaces. We must not omit, 

 that even in Gomphonemeae the primary surfaces are 

 traversed by the usual two longitudinal striae, terminating, 

 superiorly at least, in distinct apertures. 



31. NAVICULA. Individua singularia liber a, 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 Naviculeae rather than that 

 of Diatomeae 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 Fragillarieae, and still more 

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



