should have become extinct, simultaneously with the last of the Ammonites, at the termination of the Chalk formation.
Hamite.
If we imagine a Baculite to be bent round near its centre, until the smaller extremity became nearly parallel to its larger end, it would present the most simple form of that cognate genus of chambered shells, which, from their frequently assuming this hooked form, have been called Hamites. At Pl. 44, Fig. 9, 11, represent portions of Hamites which have this most simple curvature; other species of this genus have a more tortuous form, and are either closely coiled up, like the small extremity of a Spirula, (Pl. 44, Fig. 2,) or disposed in a more open spiral. (Pl. 44, Fig. 8.)[1]
It is probable that some of these Hamites were partly internal, and partly external shells; where the spines are present, the portion so armed was probably external. Nine species of Hamites occur in the single formation of Gault or Speeton clay immediately below the chalk, near Scarborough.
- ↑ Both these forms of Hamite bear the same relation to Ammonites that Lituites bear to Nautili; each being nearly such as shells of these genera would respectively present, if partially unrolled. See Phillips' Geol. Yorkshire, Pl. 1, Figs. 22, 29, 30.
Baculites and Hamites have two characters which connect them with Ammonites; first, the position of the Siphuncle, on the back, or outer margin of the shell, (Pl. 44, Figs. 5b, c. 8a, a. 10. 11, a. 12, a. 13, a.); secondly, the foliated character of the margin of the transverse plates, at the junction with the external shell. (Pl. 44, Fig. 5, 8, 12, 13.) The external shell of Hamites is also fortified by transverse folds or ribs, increasing the strength both of the outer chambers and of the air chambers, upon the same principles that we have pointed out in the case of Ammonites. (See Pl. 44, Fig. 8, 9, 11, 12, 13.)
In certain species of Hamites, as in certain Ammonites, the marginal Siphuncle has a keel-shaped pipe raised .over it. Others have a series of spines on each side of the back. (Pl. 44, Fig. 9, 10.)
