_Lingula_ occurs in the Indo-Pacific, Australia, China, Japan, and the Pacific Islands. _Glottidia_, a smaller form, with two small curved plates on the brachial and a ridge on the peduncle valve, is found on the American coast of the Pacific, and in the Atlantic. [Illustration: Fig. 5. _Lingula anatina_, removed from shell, mantle reflected, coiled arms separated slightly; _a_, mouth. (Marginal setæ omitted.) Ventral aspect, three-quarter face. ] [Illustration: Fig. 16. _Lingula anatina._ Interior of valves showing muscle scars. V. Peduncle valve, D. Brachial valve. ] Order 2.—NEOTREMATA. The _Discinidæ_ includes two genera, _Discina_ and _Discinisca_ (Fig. 7), with orbicular conical shells, of horny calcareous composition; both valves are conical in the former genus, but in the latter the peduncle valve is flattened. Sometimes the embryos settle down on the parent shells, and we see a mass of shells in various stages of growth, as in the specimen of _Discinisca lamellosa_ from Peru. [Illustration: Fig. 7. _Discinisca lamellosa._ Peru. (After G. Sowerby.) A group of old and young specimens; largest showing foramen in peduncle valve, the rest showing brachial valves. ] [Illustration: Fig. 8. Three specimens of _Crania anomala_ on a stone. Loch Fyne. ] The _Craniidæ_ form small limpet-like shells (Fig. 8) closely adherent to the rocks by the whole surface of the peduncle valve; although this valve is so named, no peduncle or foramen is found in this family. The Neotremata, like the _Lingulidæ_, are remarkable examples of persistence of type, since forms very similar to the present day _Discinas_ and _Cranias_ occur in the Palæozoic, Ordovician and Silurian strata. A piece of rock, with several specimens of _Crania anomala_ attached, is exhibited. Section II.—ARTICULATA. Order 3. PROTREMATA.—This group, formerly very abundant, is now almost extinct, the Family _Thecidiidæ_ representing the Order at the present day. _Thecidium mediterraneum_ (Fig. 9) forms little oval boxes about a third of an inch in length, shaped somewhat like a pear cut in half (peduncle valve), and with a semicircular lid (brachial valve) working on a hinge on the upper flat surface. The foramen and peduncle are absent; but between the pointed end of the peduncle valve and the hinge is an area filled in by a calcareous plate characteristic of the Protremata. [Illustration: Fig. 9. _Thecidium mediterraneum._ A, natural size. B, section through shell. Magnified. ] The brachial valve opens like the lid of a snuff-box, and shuts down on the least alarm with the rapidity of lightning. The peduncle valve is fixed on the rocks by its convex surface. The species is common in the Mediterranean in from 30 to 300 fathoms, and is also found in the West Indies.