Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/281

 Rh should have become extinct, simultaneously with the last of the Ammonites, at the termination of the Chalk formation.

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.)

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.