Dr. Wallich on the Uhizopods. 457 



tliese are described as " transitional to tlie compressed variety 

 of D. pyriformis.'''' Again, if we turn to pi. xii. of Difflugia 

 pyriformisj figs. 10, 11, 12, and 13, we shall see that thesemight, 

 without the least incongruity, have been inserted in pi. xxiv. as 

 additional, and, in reality, hetter representations of the meta- 

 morphism shown in figs. 1 1 and 12 of that plate. A dozen such 

 examples might be added to these were it necessary. I must, 

 however, draw particular attention to the very important fact 

 that these six figures also agree (as closely as any half-dozen 

 specimens of the same forms of Difilugidge can agree with each 

 other) with fig. 30, plate xvi., of my series of transitional meta- 

 morphic forms oi Diffiugia pyriformis^ to which I refer them, as 

 ih.ki first link in the chain of varieties which lead up to Dif- 

 fiugia symmetrica. The woodcuts JSTos. 3 and 4 at pp. 469, 470 

 of this paper are in reality specimens oiD. pyriformis^ so far as 

 mere form is concerned ; fig. 3 being the ordinary variety with 

 the test made up of angular mineral fragments, nearly always 

 more or less transparent. When the test is covered to this 

 extent with large and angular mineral particles of varying 

 sizes and shapes, it has passed the stage at which metamor- 

 phic action, or, in other words, the combinaton of the siliceous 

 material impacted into the yielding chitinoid basis of the test, 

 can enter into colloidal combination with it. In fig, 2 

 (at p. 468 of this paper) the metamorphic combination has 

 gone as far as it generally does in such a form j attention is 

 drawn to it now chiefly with a view to prove that the pyriform 

 or mitriform " compressed '^ shape, said to be characteristic 

 of the shell of Quadrula symmetrica^ is one of the typical 

 characters recorded of Difflugia pyriformis and its variety D. 

 compressa at p. 99 of Prof. Leidy's work. Now if we look 

 at figs. 10, 11, 12, 13 of pi, xii., representing I) ifflugia pyri- 

 formis, and figs. 4 and 12 of pi. xxiv. representing Nehela 

 collaris, the truth at once bursts on us, that the figures from 

 pi. xii. of D. pyriformis might be transferred to pi. xxiv., and 

 the figs, of Nehela collaris from pi. xxiv. to pi. xii. oiD. pyri- 

 formis^ without even an expert in the history of the testaceous 

 freshwater Rhizopods being able to assert positively that the 

 whole of the six specimens were anything else than average 

 specimens of Difflugia pyriformis. I contend tlierefore that 

 there is nothing in the shape of the test in Difflugia sym- 

 metrica to distinguish it from the test of D. pyriformis^ or 

 certain metamorphic forms of Nehela collaris of which I shall 

 have to speak hereafter in reference to another character. 



Figs. 27 to 33 of pi. xvi. appended to my paper in the 

 'Annals' for March 1864, which Prof. Leidy says I "de- 

 scribed as transitional forms of Difflugia symmetrica^'' I have 



