Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . long peduncle, and bythe equality of the valves of its shell, neither of which are perforated :the Orbicula {Disci?ia, Lam.) is sessile, and adheres by one end of ashort transverse muscle, which perforates the ventral valve of theshell, which is the flatter valve. The Terebratula {figs. 186 and 187)is attached by a short peduncle (6), which projects through a hole ina beak-shaped prolongation of the ventral valve (v), which is the moreconvex one. To the dorsal valve (d)
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . long peduncle, and bythe equality of the valves of its shell, neither of which are perforated :the Orbicula {Disci?ia, Lam.) is sessile, and adheres by one end of ashort transverse muscle, which perforates the ventral valve of theshell, which is the flatter valve. The Terebratula {figs. 186 and 187)is attached by a short peduncle (6), which projects through a hole ina beak-shaped prolongation of the ventral valve (v), which is the moreconvex one. To the dorsal valve (d) is attached the internal cal-careous process, usually in the form of an elastic loop, and called the apophysary system (a, h, c, ). The subdivision of thegenus Terebratula*, the most cha-racteristic of the Brachiopods, andthe type of the most extensivefamily of the order, is based chieflyon modifications of the internalprocesses. The foramen in theventral valve is usually more orless formedbyasmall detached partcalled the deltidium. The valves are articulated by two curved * Dim. of terehratus, Terebratula flavescens. 486 LECTURE XX. teeth, developed from the margin of the ventral valve, and receivedby sockets in the other: the joint permits only a very slight divari-cation of the valves. The viscera are situated at the part of the shell next the hinge orpeduncle, and are confined to a very small space in the rest of the interspace of the lobes of the mantle is almost entirelyoccupied by two long fringed arms, continued from the sides of themouth, and disposed in folds and spiral curves {m). The bases ofthe arms are confluent, and form a transverse fringed band abovethe mouth : a narrow parallel fold of membrane passes below themouth (7^), which opens upon or towards the mantle-lobe attached tothe perforated valve. In the Terehratula australis each arm extends outwards, advancesforwards, curves slightly inwards, and bends abruptly back
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1850
