1848.] LONSDALE ON FOSSIL ZOOPHYTES. 57 



in an able article on Spongiadse by another authority, they are con- 

 sidered as families*. It is also now admitted, that the composition of 

 Amorphozoa is not a sufficient basis for genera ; but that the ar- 

 rangement of the skeleton, and the form and distribution of the orifices 

 and pores, as well as the habitat, should be considered ; likewise when 

 possible, the nature of the gelatinous matter with the characters of 

 the ova, and many other points, will be readily suggested to the mind 

 of the experienced student. The freshwater body Spongilla has 

 been by one authority united generically with marine TIalichondriaf , 

 solely on account of its siliceous skeleton ; a union, however, which 

 has not been adopted. These remarks on the known component 

 parts of sponges have been considered necessary in an attempt to 

 approximate towards a knowledge of the Atherfield fossil. 



A flake of that body dissolved completely in diluted muriatic 

 acid, so far as the magnifying powers employed could be trusted ; 

 due care being also taken to discard adventitious particles ; and it 

 was not until a portion of the fluid had evaporated, that anything 

 resembling spicula could be detected. The microscopic needles then 

 visible were however regarded only as minute crystals of selenite, 

 due to a slight impurity in the acid. This rough experiment, in 

 conjunction with the detected structures, leads, therefore, to the in- 

 ference, that the fossil was originally a calcareous sponge ; and that 

 among existing known Amorphozoa, it resembles most nearly the 

 genus Grantia, if mineral composition were admitted a sufficient 

 basis on which an agreement could be founded. In the dense nature 

 of the opake portion, a similarity may be also noticed with Grantia 

 comp?'essa, especially when squeezed fragments of that species are 

 exainined conjointly with sections or transparent slices of the Ather- 

 field organic remain, and each is viewed under the same low mag- 

 nifier ; but when the power is sufficiently increased and applied 

 successively to the recent and extinct body, the former is shown to 

 consist of very conspicuous trifid spicula, while the latter retains its 

 minutely granular appearance ; Grantia, moreover, is described as 

 wholly destitute of a network J, while in the Atherfield fossil such 

 a structure was clearly observed, independent of the general calca- 

 reous composition, though its true nature is not presumed to have 

 been ascertained. The characters of the large or excurrent canals 

 in the greensand sponge difler markedly from the equivalent aper- 

 tures in Grantia compressa and similarly formed species ; but in 

 others which are crustaceous, as G. coriacea, there is a seeming re- 

 semblance ; nevertheless, the apparent nature of the calcareous matter, 

 and the existence of a fibrous reticulation, forbid, it is conceived, a 

 generic identification. The union of a corneous network and calca- 

 reous spicula in the Alcyonium papillosum of Lamarck has been 

 already mentioned ; but supposing that the fossil under consideration 



* Penny Cyclopaedia, vol. xxii. p. 376, col. 1, 1842. 

 + Hist. Brit. Animals, p. 524. 



X Johnston, Brit. Sponges, p. 8 ; consult also Dr. Grant's original memoir, 

 Edinb. Phil. Journ. vol. xiv. p. 339, 1826. 



