A Monograph of the Eocene Mollusca: Descriptions of Shells from the Older Tertiaries of England

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Palaeontographical Society, 1849 - Cephalopoda, Fossil - 361 pages
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Page 7 - The observations of Mr. Adams, published in the ' Zoology of the Voyage of the Samarang,' tend to prove that the shell is constructed by the female Argonaut as a nest for receiving her eggs, and protecting them from injury, resembling in some measure the rudimental capsules secreted by many marine Gastropods for the preservation of the embryo. The animal firmly retains possession of this light calcareous shell-nest by means of the broad expanded membranes of the posterior pair of tentacles ; but...
Page 16 - ... formation occurs Clymenia, which forms a link with the Goniatite of the mountain limestone, a fossil approximating, if not fully belonging to the Ammonite family. The distinctions are chiefly in the form of the septa or walls which divide the chambers of the shells. A living palaeontologist says — " As we ascend in the Palaeozoic series, we find that various of the primitive genera and species disappear, and are succeeded by other forms, distinct from, but closely allied to them; which, in...
Page 67 - H. labyrinthica. Shell conic, dark reddish-brown, body lighter; -whorls five or six, with conspicuous, elevated, equidistant, obtuse lines across, forming grooves between them; apex obtuse; lip reflected, rounded; pillar lip with a large, lamelliform, elongated tooth, which appears to revolve within the shell parallel to the suture, a smaller raised line revolves nearer to the base within the shell, but becomes obsolete before it arrives at the pillar lip; umbilicus rather large. Breadth one tenth...
Page 42 - Animal; body oblong, posteriorly rounded, and terminating in a slender membranaceous tube; head above, with an ambulatory disc ; arms, nineteen (?) on each side ;* labial tentaculiferous appendages, four, arranged round the mouth ; tentacula of three kinds, viz. ophthalmic, lamellose, two on each side ; brachial, annulose, twenty on each side; labial, annulose, twenty-four on each side; the whole body contained in the last chamber of a large multilocular shell, and affixed by two lateral muscles....
Page 40 - ... the wide cavity of Belosepia. Thus the transition from Belosepia, through Belemnosis and Belemnitella, into Belemnite will be easy and natural, and the chain of connexion between the latter genus and the recent Sepia will be complete. The principal character, however, which distinguishes Belemnosis is the aperture forming a communication between the alveolar chambers and the sac in which the shell was lodged. In all the camerated siphoniferous shells, I believe without exception, the inferior...
Page 13 - I am much disposed to believe, that in every distinct formation of shell-substance there is a single layer of membrane; and I am further of opinion that this membrane was at one time a constituent part of the mantle of the mollusc.
Page 83 - ... rudimentary lateral jaws, a large central spiral body, and a simple-edged mantle, covered by an external ovate, thin, dextral, transparent spiralshell with an ovate mouth, having a single oblique plait on the middle of the column running into the axis. " Limnsea has a small central tooth, as it were squeezed up between two very large lateral ones, each primary lateral having a very large apex internally, with a small external one, while at the edge they have altered to one thick prolonged apex...
Page 13 - ... this state they somewhat resemble the incipient form of the prismatic cellular substance. These cells may be occasionally seen in sections of the shell itself; and they will be often found in very different degrees of development even in the corresponding layers of two shells of the same species. Coupling the appearances which I have myself observed with the observations of Mr. Bowerbank, on the formation of shell, and keeping in view the general doctrines of cell-action, which I have elsewhere...
Page 49 - Sowerbyi is an exceedingly well-marked species. It is a smooth, discoidal, convex or rather lenticular shell, somewhat resembling in shape the Dax form of Aturia (Nautilus) zic-zac, but it is narrower towards the margin, which circumstance gives a triangular form to the aperture.. The septa (Tab. VIII, fig. 3) are very concave, and present on each side a broad undulation, with a deep sinus-like depression caused by a lateral lobe, more developed in this species than in N. urbanus, although not attaining...
Page 56 - Nautilus may likewise possess the additional advantage of producing a slight vacuum in the posterior parts of the chamber of occupation which is shut out by the horny cincture, and muscles of adhesion from the rest of that cavity. Whatever additional advantage the existing Nautilus might derive, by the continuation of a vascular organised membranous siphon through the air-chambers, in relation to the maintenance of vital harmony between the soft and testaceous parts, such likewise must have been...

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