Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/282

 278 (See Phillips' Geology of Yorkshire.) Some of the larger species equal a man's wrist in diameter.

The Scaphites constitute a genus of Elliptical chambered shells, (see Pl. 44, Fig. 15, 16,) of remarkable beauty, which are almost peculiar to the Chalk formation; they are so rolled up at each extremity, whilst their central part continues nearly in a horizontal plane, as to resemble the ancient form of a boat; whence the name of Scaphite has been applied to them.

It is remarkable that those approximations to the structure of Ammonites which are presented by Scaphites and Hamites, should have appeared but very rarely, and this in the lias and inferior oolite, until the period of the cretaceous formations, when the entire type of the ancient and long continued genus Ammonite was about to become extinct.

The last genus I shall mention, allied to the family of Ammonites, is composed of spiral shells, of another form, coiled