. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. INCLUSA THE BRACHIOPODA. 475 class Conchifera, there is a very curious group which should also be included in it, although established as a separate class by many naturalists. This is the group of Brachiopoba, con- taining only three genera at present known, namely, Tcrebra- Hda, Lingula, and Orbicula ; but formerly of much greater com- parative importance. These animals have all bivalve shells, differing in no essential particular from those of the Conchifera in general. The two former genera are attached, how
. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. INCLUSA THE BRACHIOPODA. 475 class Conchifera, there is a very curious group which should also be included in it, although established as a separate class by many naturalists. This is the group of Brachiopoba, con- taining only three genera at present known, namely, Tcrebra- Hda, Lingula, and Orbicula ; but formerly of much greater com- parative importance. These animals have all bivalve shells, differing in no essential particular from those of the Conchifera in general. The two former genera are attached, however, bv a footstalk, proceeding from an opening in one of the valves near the hinge, to solid substances; and in this respect they have an affinity with theTunicata. The Orbicula are attached, like an oyster, by one of the valves. They bear considerable resemblance to the Tunicata also, in the structure of the nu- tritive system—the digestive apparatus, heart, gills, &c. But in the complexity of the muscular apparatus provided for giving motion to the valves, they much surpass the highest of the other Conchifera. There are not only several muscles pro- vided for the closure of the shell, but another set to open it— an organization which no other bivalves possess. The most peculiar part of their structure, and that from which they de- rive their name, consists in the presence of two very long arms or tentacula, between the origin of which the mouth is situated. These can be projected to 'a considerable distance from the shell, or drawn in and coiled up spirally within it. They do not appear, however, to seize upon prey, but rather, by means of the cilia with which they are fringed, to create currents. Terebratula: A, valve with the spiral arms; B, valve with arms removed. which may bring food to the mouth. In the Terebratula, these arms are affixed at their bases to a very curious framework within the shell, the use of which is uncertain; but it is be- 862. How is this
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