83 
of Edinburgh, Session 1862 - 63 . 
in length, and, as is so often the case with ammonites, seem to 
have lain long in the water after the death of the animal. They 
have, however, the distinct characteristics of the Ceratites nodosus. 
These specimens have been the more carefully examined, and 
the inferences deducible from them the more keenly discussed, from 
the fact that they have been thought to offer some support to the 
Darwinian theory of transformation. Yon Strombeck and others be- 
lieve that the latest generations of the Ceratites nodosus, as exhibited 
in the highest strata of the Muschelkalk elsewhere, show a pro- 
gressive tendency to a certain aberration from the earlier type, as 
figured by Von Buch in his monograph “ iiber Ceratiten.” This 
aberration, though marked, is not sufficient to constitute, but may 
be represented as a step towards, a new species. The Liineburg 
specimens present this aberration in its widest form, while still 
obviously belonging to the species nodosus. If, therefore, the beds 
in which they are found can be attributed to the Lettenkohl, then 
a greater lapse of time is secured. To this lapse of time the change 
of form may be assigned, and thus some colour may be found for 
attributing to this same cause the whole of those minute changes 
of form which the successive species of ceratites present, and which 
so completely link them on at either end with the antecedent 
goniatites, and the succeeding ammonites. 
As to the question of form. The Ceratites of Liineburg differs 
from that figured by Yon Buch in this, that in the latter the knobs 
on the side are included in the first lobe, while in the Liineburg 
specimens the back is so much broader that the first lobe fails to 
reach so far as the knobs, and the second saddle is as it were drawn 
ofi“ the side towards the back, and it therefore, instead of the first 
lobe, thus includes the knobs. Yon Buck’s drawings, however, 
though otherwise most careful, and in this case professedly made 
from the same specimen, do not agree with one another (see fiber 
Ceratiten,” Plate I. fig. 1, and Plate II. fig. 1.) in this very respect 
of the relation of the knobs to the lobes and saddles ; and so, in 
regard to this particular point, nothing can be made of them. 
Further, it appears that in all young specimens the back is rela- 
tively narrow, and the first lobe extending round the corner of the 
back at that period of life reaches the knobs on the side ; but in- 
variably, as the shell increases with age, the back becomes relatively 
