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.

206/218 page 176

$Gallery VII. Wall-case 7. Table-case 16. W all-case 7. 176 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. preserve the ink-bag, which in (1. hrevipinnia from the Oxford Clay of Christian Malford is sometimes of great size, while the ten arms are very short—an obvious correlation. Fi-om the Up]>er Lias are also shown the similar shell of Tct(thoj)sis, ami that of Bdotcuthis strengthened by a median keel. Shells of generally similar cliaracter are found in Coccoleiithis \Trachyteiiflds\ from the Solenhofen Stone. An a<lmirable specimen preserves ]>ortions of the mantle and side-fins, and has eight well-developed arms bearing suckers ; the two long arms found in recent Decai)oda may have been present but retracted. A very large shell of this genus is at the bottom of the (Jase. In Plcsio/culhis prisen- from the same stratum the shell is reduced to a long narrow pen, with the side ex])ansions at its hinder end and quite small. The same genus occurs in the Senonian rocks of the Lebanon, whence come Plcsiotcuthis Fraasi and the allied Doratcuthis sjjrinca (Fig. SO h), both with eight short and possibly two long arms. A shell in which the phragmocone is still preserved, as in I'hragmotcuthis, but in which the guard is reduced to a thin shiny coat, is that of Pdemnoteuthis anliqua (Fig. 8(i a). There is shown a fine series of this from the ( Oxford Clay, chiefly of Christian Malford (see }). 15G). The ten short arms are well seen, and in one specimen seem to have caught a small fish. AcanilioteuiMs from the Solenhofen Stone is said to have had a shell with more reduced phragmocone and larger pro-ostracum. Specimens are sliown preserving the .arms, eight or ten in number, with well-marked hooks; the m.antle; and a membrane round the mouth like that of living Onychoteuthidie. Conotenfhis 8.7//), of which fo-ssils .are shown from hfeocomian, Aptian, and Albian rocks, had a small curved phragmocone, suggesting the end of the Ommastrephes shell (idg. 85 h). The specimen of Palaeocfopits Ncwholdi, from the Senonian of Lebanon, is the oldest fossil Octopod. There is no evidence to show from which of the races just described it may have been derived. 'With the Octopoda, which are the most highly specialised of IMollusca, and furnish some of the monsters of modern seas, we reach the end of this sketch of extinct invertebr.ate animals.$