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194 sand by the sliding motion of the two valves, using at the same time the fringes of setce, which swing promptly back and forth like a galley of oars, leaving a peculiar tract in the sand. In the motion of the setaa he noticed the impulse commencing from behind and running forward. Discina has been found attached to stones at low water mark, and dredged from depths ranging from 5 to nearly 2000 fathoms. They are very often clustered together in vast numbers, each adhering by its peduncle to the surface of the shell of its neighbour, one above the other, till they form a living mass of considerable breadth and thickness. Crania is found in great numbers adhering to stones and shells at depths of from 18 to 530 fathoms. The genera and species of the Clistenterata live at depths ranging from about half tide mark to that of 2600 fathoms. Terebratulina caput serpentis was found by the late R. T. Loweliviry attached to rocks at low water mark on a part of the Scottish coast, where the tide falls only a few feet, but the same species has been dredged alive from depths varying from 3 to upwards of 150 fathoms. Prof. Jukes got immense numbers of specimens of Waldkeimia flavescens or Australia while boating in Aus tralia among the reefs. They were merely washed by the tide, and he gathered them with his hand like limpets on the shore. M. Velain picked up a small species of Kraus- sina in vast numbers on the shore in the interior crater of the island of St Paul, the shell being alternately covered with water and left dry at every tide. Kraussina rubra, from the coast of Natal in South Africa, was described by Dr Gray as having been found attached in great numbers to ascidia and stems of sea-weeds, and Mr Jeffreys had also previously noticed a small European species similarly fixed to sea-weeds. In general, however, it may be said that the larger number of species inhabit depths varying from 5 to 300 or 400 fathoms. Several species live attached to coral reefs. Waldkeimia cranium has been obtained from depths varying from 160 to 228 fathoms. Barrett and Jeffreys state that Terebratulina caput serpent is manifested a remarkable power and disposition to move on its peduncle, and that it was incessantly opening and fold ing its brachial appendages, and drawing in and sucking in, by means of the whirlpool thus caused, every animalcula within its influence.

It is now necessary to say a few words with reference to the classification of the Brachiopoda, and in drawing up an y scheme of arrangement due regard must be paid to the extinct forms, which vastly outnumber those of the pre sent seas. The first species belonging to the class were imperfectly and quaintly described as well as figured by Fabio Columna as far back as 1606. Since then so many palaeontologists have contributed to the elucidation of the fossil species that it would not be possible to give all their names ; we must not, however, omit to record those of Linnaeus, Defrance, Von Buch, Alcide D Orbigny, De Blainville, Sowerby, Barrande, De Verneuil, Deslongchamps (father and son), De Koninck, E. Sues?, W. King, F. M Coy, J. Hall, Billings, Dalman, Dall, Fischer, Pander, C. Moore, Eichwald, Kutorga, Keyserling, Sandberger, Sequeuza, Salter, Morris, Meek, and Davidson. Various schemes of classification have been proposed, but none as yet can be said to be more than provisionally satisfactory, because before one can classify it is necessary to understand all the characters of the species one has to arrange in their more or less natural groups, and we are not yet in possession of all that necessary information. In 1853 Davidson divided the Brachiopoda into eight families, comprising twenty-four genera and about as many sub-genera, but during the years that have elapsed from that to the present time, about seventy more genera and sub-genera have been described, so that as many as one hundred and twenty-three so-termed genera have now to be classed into their respective families, a task which has not yet been satisfactorily accomplished. It is, however, very probable that the number above given has been exaggerated, and that when our knowledge has increased, some of them will have to be placed among the synonyms. It will be necessary in every scheme of classification to admit the two great divisions Tretenterata and Clistenterata. The would comprise the families Lin- gulidce, Discinidce, CraniaJcc, Trimerellidce, and perhaps one or two others. The would include the families Tcrc- bratididw, Tkecidcedce, Spiriferidce, Rhynchonellidce, Pcnta- meridce, SlrophomeridcE, Orthidae, Productidce, and perhaps two or three others that will have to be characterized. By far the larger number of described genera and species would find their place in this last great division and the above-named families. We will now very briefly notice some of the characters of the families above indicated.

—Family 1. Lingulidæ.—Shells generally either oblong or circular, with a peduncle, sometimes of considerable length, passing out between the valves or through a narrow channel in the hinge margin ; texture horny no calcified supports for the labial appendages ; the fleshy spiral ceils directed upwards. This family would comprise the following genera: Lingula, Lingulella, Lin- gulops, Lingulepis, Glottidia, Monobolina, Obolus, Obolella, Dignomia, Schmidtia, Acritis, Volborthia, &amp;lt;fec. Lingulella is one of the oldest known types of animal life, while Lingula appeared for the first time about the middle of the Cambrian period, and has continued to be represented up to the present time.

Family 2. Discinidæ.—Shells more or less circular or oval shaped, attached by a peduncle passing through a foramen in the ventral valve ; shell calcareous or horny ; setae extremely long, barbed with cilia of great length ; labial appendages fleshy, curved backwards, with small terminal spire directed downwards as in Crania (fig. 11). Genera .Discina, Trematis, Discinisca, Kutorgina (1), Acrotrata (]), SipJionotrata (T). Discina appeared about the middle of the Cambrian period, and has continued to exist up to the present time.

Family 3. Craniadæ.—Shells orbicular or limpet-like, entirely free or attached by a greater or lesser extent of the under surface of their ventral valve ; labial appendages spirally coiled, directed towards the bottom of the dorsal valve (fig. 11); shell calcareous, perforated by minute canals. Genera Crania, Craniops, Craniscus, Pholidops, The genus Crania appeared for the first time during the Silurian period, and has continued to be represented up to the present time.

Family 4. Trimerellidæ.—Shells transversely or longitu dinally oval ; ventral valves usually the largest and flattest, with a more or less developed beak and area ; ventral valves generally the most convex ; hinge rudely or faintly dentary; all the genera are provided with a solid or vaulted muscular platform in the interior of both valves ; no calcareous support for the labial appendages ; shell calcareous, and in two of the genera very massive. All the forms are extinct. Genera Trimerella, Monomer ella, Dinobolus. The species of this family are restricted to the Silurian period.

—Family 5. Terebratulidæ.—Shells very variable in shape, with a prominent beak, truncated by a circular perforation, partly completed by a deltidium in one or two pieces ; labial appendages united to each other by a membrane, variously folded upon themselves, and in some genera spiral at their extremities. These appendages are entirely or partially siipportecl by a calcified process, 