Dr Fleming on the Natural History 
0.005 of a millimetre, presented facets which replaced the termi- 
nal edges, that formed the junction of the prism with its base. 
They could not, however, discover any crystals with pyramidal 
summits 
Having thus examined the form of the icy crystals, the tra- 
vellers resumed the lights ; and having placed them in the most 
clear and best crystallized parts of the cavern, they congratulat- 
ed themselves in having* produced, amid the ruins of the caverns 
of the desert of Fondeurle, an effect worthy of all that the ma^ 
gical palaces of the Thousand and one nights could present to- 
the richest and most brilliant imagination. 
The floor of ice is occasionally dug up, and carried to the 
nearest towns, and even to Valence, which is more than two* 
leagues distant. 
Aet. XIII. — Observations on the Natural History of the Ser~ 
tularia gelatmosa of Pallas. By John Fleming, D.D, 
F. B. S. E. and M. W. S. Communicated by the Author. 
Although the penetrating genius and perseverance of 
Ellis elucidated the characters of many species of Sertulariae 
which occur on our shores, much yet remains to be done, in or- 
der to complete the history of this beautiful tribe of zoophytes. 
Since the days of our British Lynceus, however, few observers 
have turned their attention to the study of these animals, so as 
to make us acquainted with new species, or to extend our know- 
ledge of the economy and distribution of those which have al- 
ready been described. 
In 1800, Mr Adams published a description of what he con- 
sidered a new species, and which he termed S. imbricata, in 
the 5th Vol. of the Linnean Transactions, p. 11. Tab. % 
flg. 5. — 11. M. Lamouroux, however, in his valuable work 
* Hexahedral crystals of ice have also been observed by M-. Hassenfratz and Mr 
Scoresby ; and we have been informed by Mr Scoresby, that when thick masses 
of icc were left to thaw upon deck, they always presented the rude outline of 
six-sided prisms. Rome de Lisle, M. d’ An tie, and Mr Scoresby, have also detect- 
ed octahedral crystals, formed of two four-sided pyramids. These crystallisations 
are strictly conformable to the optical structure of ice, as ascertained by Dr 
Brewster. See Phil. Trans. 1818, p, 211., and Edin. EncycL Art. Ice. 
