With regard to these alated species of _Uniones_, it is necessary to observe that they are also "_adnate_," as it is termed; the two valves being joined to each other by the dorsal edge of the expanded parts, and united so completely in substance with each other, that they cannot be separated without being broken. Many other terms are used to express difference in Bivalves, but being generally applicable to Univalves and Multivalves, as well as to them, they will be found explained at large in the alphabetical part of the work. MULTIVALVE SHELLS. These are of three different kinds; first, the "_dorsal_," as they are termed by Linnæus, because they form a ridge in the back of the animal. They are composed of eight pieces, or separate valves, placed in a longitudinal series, being joined to each other by inserted lamina, and named _Articulata_ by De Blainville, on that account. The genus Chiton is the only example of this kind of Multivalves. [Illustration: Fig. 84, 85, Chiton. _a_, anterior; _p_, posterior; _d_, dorsal ridge; _l l_, lateral areas of the valves; _c c_, central areas; _i i_, inserted lamina; _m_, margin.] The second kind, M. De Blainville terms the _lateral_ bivalves, the pieces being placed in pairs on each side of the animal; these compose the "Pedunculated Cirripedes." [Illustration: Fig. 86, Anatina.] They differ considerably in the number and arrangement of the valves; the small ones, which are found near the peduncle in some species, are sometimes termed accessary valves; those which form the edge through which the bunch of Cilia protrude, are termed _ventral_, and those on the opposite side _dorsal_. The extremity joining the peduncle is the basal, or anterior; and the upper extremity is the apsiral, or posterior. The peduncle is the medium of attachment to submarine substances, to which this well known tribe of shells adhere. The third kind are termed _coronular_ by De Blainville, and compose the order Sessile Cirripedes of Lamarck; they consist of a number of valves placed against each other side by side in a circle, supported on a plate, or tube, or cup, and closed by an operculum composed of two or more valves. The _basal support_ is sometimes thick and flat, sometimes forming an elongated tube, and sometimes hollowed out into a cup. In other species it is altogether wanting. The operculum always consists of more than one piece, generally of two pairs: they are either articulated to each other by serrated edges, and placed against each other conically, as in Balanus, or they lie flat in two pairs against each other. Through the ventral pair the _cirrhi_ protrude.