A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) ... / With 7 plates and 96 textfigures.
- British Museum (Natural History). Department of Geology
- Date:
- 1911
Licence: In copyright
Credit: A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) ... / With 7 plates and 96 textfigures. Source: Wellcome Collection.
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![In the Lower Lias of Dorset are still found very large ])hragraocones, but other specimens show the Belemnite type fully”ileveloped, with pro-ostracum, ink-bag, and hooked arms. Of Bclemnites clongatus there is the fine specimen described by Huxley in the Alonographs of the Geological Survey and Sowerby’s original specimen from Crick tunnel near Daventry. The Middle Lias of Charmouth has yielded the slender Xiphotcutliis elongata, also described by Huxley. From the Upper Lias of Alderton, Gloucestershire, comes a well- preserved pro-ostracum. A monster phragmocone of the Bajocian species Bclemnites gigantcus comes from Germany. The Oxfordian of Trowbridge and Christian Malford in Wiltshii-e furnishes a large series of B. Oioenii. Among Cretaceous belemites, Buvalia dilatata is remark- able for its guard, swollen in one direction and flattened in the other. Actinocamax is the usual form from Cenomanian to Senonian, being joined by the similar Belemnitella in the latter Age. The belemnites did not die out at the close of the Cretaceous Epoch, but they changed in character. Styraco- tcuthis orientalis from the Eocene of Syria is still of the older type, but in most the guard was reduced in length, thickness, and calcification. Vasseuria from French Eocene rocks has such a slender yet relatively short guard. In Bcluplcm and Belopteriva the guard is short and somewhat swollen at its end, which makes a slight angle with the phragmocone; in the former it expands at the sides into two wings. The latter genus is not far removed from the Miocene Spiruliroslra, already described (Fig. 85 h). In a later genus Spiridirostrina (not exhibited) the guard is more reduced, and in the modern Spinda it has disappeared (Fig. 85 c). Another line of evolution leads, as previously explained, from Beloptem to Beluscpia (Fig. 85 d) of which many specimens from the London Clay and Bracklesham Beds, are shown. Sepia itself is exhiluted from later Tertiary rocks (Fig. 85 e). Of those sheathed forms in which the calcification of the shell underwent a gradual reduction, the earliest known is Phragmoteidhis from the Upper Trias. The next in age is Geotevthis, of which large specimens from the Lower Lias of 1 )orset are exhibited. These and the smaller specimens from the Upper Lias of Wurtemberg and Normandy show an expanded pro-ostracum, divided lengthwise into three areas, and with no trace of a phragmocone. Many of these Gallery VII. Wall-case 8. Table-case 16. Table-ease 16. Wall-case 7. Wall-case 7.](https://iiif.wellcomecollection.org/image/b24863841_0205.jp2/full/800%2C/0/default.jpg)
