The first we give is the _Ammonites Eudesianus_ (Fig. 1), which is found in the inferior Oolite, a variety of the sandstone rocks; the specimen from which our illustration is taken being from the sandstone rocks of Caen, so well known in this country from the great quantity employed in our architectural ornaments. This example is remarkable for the perfection of the spiral lines and the beautiful disposition of the ribs or elevated portions, which serve to strengthen the delicate chambered shell.
The _Ammonites cordatus_ of Sowerby (Fig. 2) is distinguished by a spiral of a different order from that of _Eudesianus_. Its ribs forming graceful waving lines, and terminating in a denticulated edge, give a very symmetrical character to the architecture of this variety.
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.
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.