conch if era

[Lat. concha =a conch, i cor. nective, and fero =to bear.] 1. Zool .: Lamarck's designation now generally adopted for the great cla of Mollusca containing the species which po e ordinary bivalve shells. Cuvier arranged the Conch if era with Salpa and the naked mollusks into a cla Acephala-i.e., Headle Animals-so called because they no apparent head, but a mere mouth concealed in the bottom or between the folds of their mantle. He placed them in an order Acephala Testacea, distinguishing their unarmored a ociates as Acephala Nuda. From their po e ing four branchial lamelle leaflets, De Blainville called them Lamellibranch i at a, a name still much in use; it is the designation Profe or Huxley retains for the cla . Their body is included within a mantle or pallium, formed by a prolongation of the dorsal intoguments; there is a well-developed heart, generally with two auricles and one ventricle, or with one of each or even two of each. Some have a conspicuous foot. They have bivalve shells of the normal type, which as a rule have the right and left valves nearly of the same size and shape, and both more or le in equilateral, the anterior being much shorter than the posterior side. This distinguishes them from the Brachiopod a, in which the bivalve shells are as a rule unequal in size, but each singly equilateral. [BRACHIOPOD A.] The valves of a Conchifer are bound together by an elastic ligament, and are jointed by a hinge furnished with interlocking teeth. Near each hinge is an umbo, i . e., a bo or beak, which was the point whence the growth of the shell originally took place. The length of a valve is measured from the anterior to the posterior side, its breadth from the dorsal margin to the base, its thickne from the center of the closed valves. Bivalve shells are said to be shut when the valves fit exactly, and gaping when they cannot be completely shut; the outer side has often ribs radiating the umbo to the 1031 country from abroad. -ια.] IMG:content-0474.png:[blocks in formation] IMG:content-0475.png:[blocks in formation] 2. Palæont.: Fo il bivalves are found in most o, and a given straight line A B, any number of pairs sedimentary rocks. They are somewhat rare in the of different conchoids can be described by varying earlier formations, but go on to increase through the length QP. Moreover, the shapes of all such the Secondary and Tertiary Periods, reaching their curves will vary according to the length of QP. maximum in the presente reaching times Thus, if op is le than the perpendicular from o more numerous in the Newer Tertiary than in the oldest geological systems. ( S. P. Woodward. ) con-chif-er-ous, a . [Lat. concha (q. v.), i connective, fero to bear, and Eng. adj. suff. -ous .] Bearing a shell. ( Pen . Cycl.)