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

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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$repetition of outward form at diflerent epoclis has already Gallery been noticed among the Brachiopoda (p. 115). Among VIII. lamellibranchs from the same rocks are Alectryonia, Lima, Ctenostrcon, Inoceramus, and tlie large THchitcs with its tluck shell, a favourite haunt of LitJwdomiis, as various specimens show. Another specimen shows a Lithodovnis burrow in the door of the Oolitic sea, here formed of black Carboniferous Limestone. Then follow many species of Trigonia, Astarte, Pholadomya, Ceromya and other genera. Among all these specimens may be noticed others from the Ironstone of Duston, Northamptonshire, and from the Collyweston Slate. In Yorkshii'e the Bajocian series includes beds of estuarine origin, furnishing such forms as Unio and Anodonta. The lamellibranchs from the Lias are arranged under Table-ease the three divisions of that marine formation: the Upper, of Toarcian age, the Middle, of Pliensbachian, and the Lower, of Sinemurian. Here one should notice Lcda ovum, which gives its name to a horizon in the Upper Lias, Volsclla \ALodiola'\ scalp'um from the Middle and Lower Lias, the very familiar Griyphaea incurva, and the equally massive Hijypo- podmm 2)onderosiim, both from the Lower Lias (Pig. 72). b Fig. 72.—Lamollibranch shells from the Lower Lias, a, Jlippopodinm ponderostan; b, Gryphxa incurva. Natural size. Oxytoma [Avimla] cygnijws, from the Cleveland ironstone beds of Yorkshire is a fine shell. The gastropods are all placed together, since they are few in number, and nearly all com- prised within three genera : Eucyclus, Cryptacnia, and Plenro- iomaria (Fig. 73). This last contains some large shells, those of r. anglica being most numerous. Trias. The Mollusca come chiefly from the Rhaetic$