The distinctness of the fossils of the coralline crag arises in part from higher antiquity, and, in some degree, from a difference in the geographical conditions of the submarine bottom. The prolific growth of corals, echini, and a prodigious variety of testacea, implies a region of deeper and more tranquil water; whereas, the red crag may have formed afterwards on the same spot, when the water was shallower. In the mean time the climate may have become somewhat cooler, and some of the zoophytes which flourished in the first period may have disappeared, so that the fauna of the red crag acquired a character somewhat more nearly resembling that of our northern seas, as is implied by the large development of certain sections of the genera _Fusus_, _Buccinum_, _Purpura_, and _Trochus_, proper to higher latitudes, and which are wanting or feebly represented in the inferior crag. Some of the corals of the lower crag of Suffolk belong to genera unknown in the living creation, and of a very peculiar structure; as, for example, that represented in the annexed fig. (148.), which is one of several species having a globular form. The great number and variety of these zoophytes probably indicate an equable climate, free from intense cold in winter. On the other hand, that the heat was never excessive is confirmed by the prevalence of northern forms among the testacea, such as the _Glycimeris_, _Cyprina_, and _Astarte_. Of the genus last mentioned (see fig. 149.) there are about fourteen species, many of them being rich in individuals; and there is an absence of genera peculiar to hot climates, such as _Conus_, _Oliva_, _Mitra_, _Fasciolaria_, _Crassatella_, and others. The cowries (_Cypraea_, fig. 147.), also, are small, and belong to a section (_Trivia_) now inhabiting the colder regions. A large volute, called _Voluta Lamberti_ (fig. 150.), may seem an exception; but it differs in form from the volutes of the torrid zone, and may, like the living _Voluta Magellanica_, have been fitted for an extra-tropical climate. [Illustration: Fig. 148. _Fascicularia aurantium_, Milne Edwards. Family, _Tubuliporidae_, of same author. Coral of extinct genus, from the inferior or coralline crag, Suffolk. _a._ exterior. _b._ vertical section of interior. _c._ portion of exterior magnified. _d._ portion of interior magnified, showing that it is made up of long, thin, straight tubes, united in conical bundles.] [Illustration: Fig. 149. _Astarte_ (_Crassina_, Lam.); species common to upper and lower crag. _Astarte Omalii_, Lajonkaire; Syn. _A. bipartita_, Sow. Min. Con. T. 521. f. 3.; a very variable species most characteristic of the coralline crag, Suffolk.] [Illustration: Fig. 150. _Voluta Lamberti_, young individ.]