Fig. 3.
The Ammonites cristagalli ([Fig. 3]), in which we have an arrangement of the convolutions not very unlike the last-named species, differs from it in the disposition of those folds which form the supports of the arch of the shell, by which a very charming though simple character is obtained.
The Ammonites muticus ([Fig. 4]), found in great abundance in the marls of the Lias, is remarkable for the very curious arrangement of tubercles or spines, which are formed by the elongation of the folds of the shell. Notwithstanding the general defect which arises from the repetition of angular lines, we have in this shell an example of the harmony which may be produced by them when arranged upon a uniform system. The radiating effect of these tubercles ranged around the involutions of the shell is very pleasing.
Fig. 4.
The Ammonites Grenouilloxi ([Fig. 5]) offers another variety, which shows the folds gradually being elevated, as these approach the mouth of the shell, into bosses, by which, of course, increased strength is secured where the shell becomes more open, and consequently weaker; at the same time they give a pleasing variety to the form of the shell itself.
The Ammonites contrarius ([Fig. 6]) presents many distinguishing characteristics, which are important to the naturalist as distinctive markings, and furnish the artist with a variety of simple elegance which deserves his study. The peculiar arrangement of the ribs, curving off right and left from a line running along the centre of the shell, gives rise to the formation of a series of festoon-like ribs, which add much to the general beauty of this species.