ANIMAL NATURE OF DIATOMEiE. 377 



in the other, of the two principal surfaces; a character 

 which reappears in various genera of stomatic Diatoraese. 

 Abstracting this character, the Himantidia would be 

 referable rather to the family of Fragillariese, with which 

 they seem to have a greater affinity. 



4. Mebidion. — Individua cuneiformia, prismatico-rec- 

 tangula, in corpuscula flabelliformia vel fascias spirales 

 arete conjuncta. StricB transversales validce, pewits. 



Kiitzing compares the Meridiese to the Gomphonemese, 

 which they really resemble, in the cuneate form of their 

 single frustules, when viewed in front. But Gompho- 

 nemese have a median aperture, and interrupted transverse 

 striae, on account of which they belong to another order. 

 In the order Astomaticse, the author himself quotes the 

 Odontidia as allied to this genus ; but the Synedrce ap- 

 pear to me to approach it still more nearly; from these 

 the Meridia in like manner rather differ in their cuneate 

 form — which is inconstant, — by their ovate obtuse figure 

 at the one and their acute figure at the other extremity 

 of the lateral surfaces. The observation of M. Zinckem 

 on the vittse, whose presence is inconstant, becomes 

 very important. This fact proves, in my opinion, that 

 there is no foundation in truly natural characters for the 

 primary distinction which Kiitzing establishes between 

 the vittated and the simply striated Diatomese, by which 

 so many natural affinities are openly transgressed, and so 

 many forced alliances are effected, as we shall soon per- 

 ceive. In the scanty state of our actual knowledge re- 

 specting the true organisation of these beings, it is im- 

 possible to establish a natural classification of them. In 

 order to deviate from this as little as possible, it would 

 be requisite to consider all the characters collectively, as 

 we do in all other beings, whether animal or vegetable. 

 And every distinction based upon a single character, be- 

 sides being purely systematic, loses all value as a facility 

 for classification so soon as exceptions occur, as in the 

 present instances. Kiitzing says that at first the internal 



