127 
gratulating myself on having declined the arduous attempt of adapt- 
ing a nomenclature to the substances examined in this volume, or of 
disposing them in a systematic arrangement. Even to one who possessed 
all the necessary qualifications, success, in the present state of our 
knowledge, could not be assured. For such is the variety of form and 
of organization discoverable in these substances, as to mock all en- 
deavours at arranging them, or even comparing them with any known 
recent substance. 
Analogy, indeed, proves their existence to have depended on the 
powers of animal life, but it seldom helps us any farther ; since, with 
respect to many of them, we can find no corresponding species nor 
genus under which known existing beings are disposed which will 
also allow of their admission. New terms must therefore be also re- 
quired to designate these hitherto unknown substances; but these can 
neither be formed nor applied, until illustrative specimens and farther 
observations have supplied a more correct knowledge of these sub- 
stances, and of the circumstances by which their relationship with each 
other should be determined. 
These observations particularly apply to the fossils which have been 
treated of in this letter ; since considerable difficulty must occur in 
the endeavour to arrange them, either according to their figure or their 
external structure. If the fungiform or cup-like figure were to be taken 
as the distinguishing character, we should then find that under this 
form would be classed substances, differing very materially in their struc- 
ture. The fungiform fossil, Plate VIII. Fig. 5, is formed of lamella? 
connected with each other by inosculation. The one, Plate XI. Fig. 
7, is composed of lamellae perpendicularly disposed, and so con- 
nected by small transverse septa or processes as to produce po- 
lygonal terstices. The specimen, Plate XI. Fig. 5, from France, 
is formed of innumerable tubuli, extending horizontally from the 
inner to the outer surface ; their bases being on the outer, and their 
other, the open terminations, being on the inner surface. Lastly, the 
