382 Dr. W. B. Carpenter on the Polytremata. 



found, especially in the spreading forms designated by Mr. 

 Garter as P. utrtculare, to be capacious chambers bearing a 

 strong general resemblance to those of Carpenteria. 



2. That the canals and chambers of Polytrema often con- 

 tain Sponge-spicules, which are also not unfrequently incor- 

 porated with their walls ; so that, as there can be no reasonable 

 doubt of the accidental nature of the inclusion of these spicules 

 in the interior of Polytrema, the probability is strong that 

 their presence in Carpenteria is to be accounted for similarly. 



This probability was further confirmed to me (3) by the 

 examination of specimens of the typical Carpenteria that 

 proved to be entirely destitute of these spongeous contents, 

 which, on the hypothesis of their " hybrid " nature, they 

 ought always to exhibit. 



I entirely and unreservedly surrender, therefore, the idea 

 that Carpenteria has any affinity to Sponges, and fully admit, 

 with Schultze and Carter, its affinity to Polytrema. But I still 

 demur to that extinction of Carpenteria as a generic type 

 which Mr. Carter proposes ; and I trust that, in specifying my 

 reasons for its retention, I shall not be thought to be influenced 

 by any undue preference for the name which Dr. Gray com- 

 plimented me by assigning to it. 



If we abandon, in the taxonomy of Foeaminifera, every 

 generic type which can be shown to have a close or even a 

 continuously gradational affinity to some other, we shall be 

 thrown back into hopeless confusion. It is absolutely necessary, 

 for the natural grouping of their multiform varieties, to have 

 some basis of arrangement ; and this seems best obtained by 

 adopting as genera those strongly diversified types which are 

 capable of most definite characterization by fundamental 

 differences in plan of growth, and by regarding these as 

 centres round which the less-differentiated forms may be 



having been observed by me in my researches on the sti-ucture of the 

 shells of Mollusks. Dr. Gray, however, agreed with me in thinking this 

 improbable, for reasons which will be presently stated " (p. 565). Among 

 these reasons, it is now somewhat amusing to find tlie statement of Mr. 

 Denis Macdouald, that, in the voyage of H.M.S. 'Herald' in the Aus- 

 tralian Seas, " he met with various forms of branching Sponges, possessing 

 a peculiarly solid calcareous skeleton, and in many instances appearing to 

 present the same kind of transition from Sponges towards Foraminifera, 

 that, if my view be correct, is afforded by Carpenteria from Foraminifera 

 towards Sponges." These specimens having been kindly placed in my 

 hands by Dr. Macdonald at a subsequent time, when I was investigating 

 the structure of Polytrema, I at once recognized them as very character- 

 istic representative.^ of that tj'pe, incrusted with a parasitic Sponge, which 

 I placed in Mr. Carter's hands for description ; so that this supposed link 

 between Sponges and Foraminifera gave way a^ soon as it was properlv 

 tested. 



