206 DESCRIPTION OF {JPolyfjastrica. 



M. Agassiz, on the contrary, would elevate them among the Gm- 

 teropoda. (Annal Nat. Hist., 1850, p. 156.) 



The genera are related to each other as follows : — 



Changeable processes / Lorica spherical or tun-like Difflxipia. 



radiant, < Lorica a flat spiral Spiriilina. 



! 



generally numerous ( Dish or shield-shaped Arcella. 



Changeable processes broad and undivided Cyphidium. 



Dujardin divides the Rhizopodes into two sections, According to 

 the form of the variable expansions, " The first section corresponds 

 to the family Arcellina of Ehrenberg, and comprehends those species 

 provided with short thick expansions, rounded at the extremity. 

 Such are the Bifflugice, possessing a flexible membi-anous lorica, 

 without visible texture, mostly of globular form, whence radiate 

 the expansions : such too, are the Arcellce, having a discoid lorica, 

 flattened on the side, along which it moves (the plane of reptation), 

 where is a central round opening, from which the expansions proceed, 

 the latter lying thus between the shell and the surface, along which 

 it glides. The lorica is, moreover, brittle, often reticulated, or 

 areolated, and indications of a spiral ; not a symmetrical arrange- 

 ment present. The second section much larger, comprises all th 

 varieties of form, presented by filiform expansions, very fine at the 

 extremity. Of these varieties I make three tribes ; the first dis- 

 tinguished from the Difflugim only by the slender character of the 

 expansions ; however, in one genus of this tribe Trinema, the opening 

 is lateral ; and certain species, forming the genus Euglypha, have a 

 lorica beset with tubercles, or areolae, disposed spirally ; whilst the 

 third genus Gromia, has a spherical membranous shell, and very long 

 and branching expansions." 



The remainder of the Rhhopodes, as described by Dujardin, are 

 located by other authors with the Polythalamia, they are marine 

 animals, having a calcareous shell, mostly very delicate and elegant, 

 and presenting a miniature, as it were, of the Nmitili and Ammonites, 

 but always divided into many cells (chambers.) Out of these 

 beings, Dujardin constitutes two other tiibes of his so-called Shi%o- 

 podes : one represented by the single genus Miliola, which, like 

 Gromia, and the other examples of the first tribe, has but a single 



