332 Dr. Wallich on the Rhizopods. 



toiy reasons for cancelling my title to priority and superseding 

 the generic position to which I referred them shall have been 

 produced than those offered in Prof. Leidy's volume. 



In my observations on the Difflugian Rhizopods, in the 

 ' Annals ' for March 1864, above referred to, I endeavoured 

 to show that the entire series of Difflugian tests represented in 

 my plates are constructed by animals which, with no known 

 exception, are generically as well as specifically identical. 

 There is nothing improbable therefore in the assumption that 

 the entire series in their earliest condition, that is to say 

 when the chitinoid exudation of which the test is entirely 

 composed makes its appearance around the sarcoblast, are 

 identical in form. When we study forms obtained from a 

 sufficiently wide geographical area we find many previously 

 existing intervals between varieties bridged over; and if 

 we note the differences in the external conditions by which 

 the animals are surrounded, whether of locality or climate, 

 we are able, generally speaking, to trace some relation be- 

 tween the peculiarities of the varietal forms and the physical 

 agencies which have helped to produce them. But in the 

 cases under notice, neither in the structure nor the degree of 

 organization of the animal itself, nor in the outward figure of 

 any of the forms of test, are there any differences to be de- 

 tected which could distinguish them generically from their 

 exact prototypes and counterparts in already well-known and 

 established typical Difflugian forms. For, as I have always 

 maintained, the changes brought about in the external 

 characters observable in the tests of the new varieties 

 described by me in the ' Annals ' for March 1864, are 

 purely dependent on contact of the chitinoid bases of the 

 tests with materials present in the medium by which they 

 are surrounded, and therefore ought not to be employed for 

 generic or specific subdivision. 



A great deal of additional evidence in the same direction 

 might be now adduced from my previous writings did space 

 allow. Before proceeding further I must therefore confine 

 myself to offering a few brief remarks bearing directly on 

 what has gone before. 



Without the production of any satisfactory reasons for his 

 statements or for taking such a step as giving a new generic 

 name to Difflugia symmetrica^ which, as he himself admits, 

 had been first described by me, Prof. Leidy thus defines the 

 new genus he has created under the name of ' Quadrula :' 

 — " Shell compressed pyriform, transparent, colourless, com- 

 posed of square plates of chitinoid membrane arranged in 

 transverse or more or less oblique series, in consecutive or 



