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me that the remaining species indicated by the above authors, 

 although embracing extreme limits of form, may yet be referred 

 to the endless variations in shape that are encountered when 

 a very numerous assemblage of these fossils is made the basis 

 of study. Nor have I observed that the types upon which the 

 above species rest, are repeated with sufficient frequency and 

 exactness to render their provisional retention a matter of 

 conventional utility. I am disposed therefore to bring together 

 under the provisional name, Rhizo-spongia polymorpha, the 

 Spongia plana, capitata, osculifera, marginata, convoluta, radi- 

 ciformis, terebrata, catablastes, fastigiata, sepia-formis, ampulla, 

 Siphonia clava, and Siph. anguilla. 



The mineral condition of these fossils is unfavorable to the 

 detection of the spicula which in their living state might 

 doubtless have been recognised, and upon which perhaps data 

 might have been founded for specific determinations. The 

 distribution, number and forms of the oscula with which their 

 surfaces are often studded, exhibit no constant relation to the 

 varieties of configuration shewn by the sponges themselves. 

 The main canals for the passage of water through the interior, 

 which have been thought to afford grounds for the establish- 

 ment, among fossil sponges, of the genera Choanites and 

 Siphonia, furnish no tangible characters for the location of the 

 Bridlington fossils, within the limits to which these generic 

 types are restricted. The nearest allied forms, among recent 

 sponges, occur in Australia and New Zealand, the principal and 

 only well marked differential feature that I can detect, consisting 

 in the distinctly defined root-like processes sent off at the base 

 in the fossil species; and though I may be reminded that in 

 the development of these parts we see an adaptation of the 

 organism to the special physical conditions which obtained at 

 the bed of the cretaceous sea, not necessarily associated with 

 any other modifications of structure, — Sponges, like the En- 

 crinites of that period, requiring to be rooted in the chalky 

 mud upon which they grew, — still the name Rhizo-spongia 

 may be used provisionally, until further light is thrown upon 

 a class of fossils which unquestionably constitute one very 

 remarkable feature in our local Geology. 



