TO GEOLOGY. 197 



is much better than that of Goldfuss, and apparently has 

 pores.* 



The genus Turbinolia seems to be more diffused through- 

 out the different Formations than any other of the Polypi. 

 In Great Britain it has been observed in the Mountain 

 Limestone, Coral Rag, Gault, London Clay and Crag. 

 Lamarck describes eight species, and Goldfuss nine, six of 

 which are new. 



I am not aware that any have before been observed in 

 our Formations. 



Nucula magna. Plate 6. Fig. 211. 



Description. It is ventured to place this name upon the 

 fragment of a Nucula, which differs on the exterior, very 



* Since the above was written, I have had the advantage of examin- 

 ing several specimens of the crispa and sulcata, in the fine collection of 

 P. A. Brown, Esq., who has recently received, from M. Alexander 

 Brogniart, most of the Tertiary fossils from the Paris basin. 



These specimens of the sulcata were observed with the same micro- 

 scope to which those of the pharetra were submitted, and pores, similar 

 to those described above, were distinctly observable. This character 

 seems to have escaped Goldfuss, as well as Lamarck, and I do not know 

 that it has been before observed by others. The relative position of the 

 ribs of the two species are very similar. In the sulcata they seem to be 

 more lamellar, and in the lower part are, in the two specimens exa- 

 mined by me in Mr Brown's cabinet, somewhat crenulate, which is not in 

 the least the character of the pharetra. In the crispa there are no pores ; 

 in this character it agrees with our Maclurii, Stokesii, and Goldfussii; and 

 I would propose that the genus should be divided into two sections, one 

 with exterior pores, the other without. 



