458 Dr. Wallich on the Rhizopods. 



already shown have nowhere been so described by me. Those 

 figures represented forms which were regarded by me in 1864 

 (and I have certainly not yet seen any reason fornot so regarding 

 them) as fairly typical varieties around which every heretofore 

 known published variety of the metamorphic aeries might 

 with propriety be grouped. These seven types, with Bifflugia 

 symmetrica^ seem to me to cover the whole of Prof. Leidy's 

 NehelfBj excepting the horned varieties, but only as varieties. 

 To make species, even in the widest sense, on such a basis 

 can, I think, hardly be considered in keeping with the spirit 

 of modern classification as applied to the Protozoa. 



The next characters given of Quadrula are : — " Shell trans- 

 parent, colourless, composed of thin* square plates of chitinoid 

 membrane arranged in transverse or more or less oblique series, 

 in consecutive or alternating order. . . . The general arrange- 

 ment is like that of tiling with variable regularity. . . . They 

 [the plates] are not entirely disposed with the symmetry ex- 

 pressed by their name, for frequently smaller plates break the 

 regular succession of larger ones, and sometimes one angle of 

 a plate replaces that of a contiguous one." — Op. cit. pp. 142, 143. 



I have already ventured to express the opinion that Prof. 

 Leidy's views as regards the test of Diffiugia symmetrica (or, 

 as he would prefer to call it, ^^ Quadrula''^ symmetrica) being 

 " composed of thin square plates of chitinoid membrane " is 

 erroneous, so far at least as I can speak concerning my own 

 specimens, which, I may add, have been procured over a toler- 

 ably wide geographical area. Of course Prof. Leidy's 

 specimens may be quite correctly described, inasmuch as the 

 degree of consolidation attained by every test of the kind in 

 which there is an admixture of siliceous or any other soluble 

 mineral substance with the chitinoid basis, must depend on 

 the quantity of that substance present in the water or mud of 

 the particular locality in which it was produced. But, for 

 reasons about to be assigned and which are gleaned from 

 Prof. Leidy's own statements, it appears in the highest degree 

 improbable that the " square plates " in Quadrula can 

 be truly described as being " composed of chitinoid mem- 

 brane " — if we are to understand the term ^^ chitinoid ^^ in 

 the sense in which he applies it to the tests of certain 

 varieties of Nehela and Hyalosphenia^ namely, as being exclu- 

 sively composed of hardened sarcode altogether unconsoli- 

 dated by any mineral ingredient which has entered into 

 colloidal combination with it. Thus Prof. Leidy describes the 

 tQQi oi^^ Hyalosp)henia cuneata^' a member of another very inter- 



* The word '' thm " was, by a mistake of mine, omitted at p. 332 of the 

 'Annals ' for November, line 2 from bottom. 



