Note 429 — Chapter XVIII · PALAEONTOLOGY OF THE BRACHIOPODA

The results of the investigations of King (Ann. Mag. Nat. Hist., 4th ser., vol. xii., 1873) and of Brooks (Chesapeake Zool. Laboratory, Scientific Results, p. 35, 1879), and the simple nomenclature of these authors are here followed in preference to those of others, owing to the difference of opinion amongst anatomists of the functions and homologies of the muscles. The lateral muscles enable the valves to move backwards and forwards on each other; the centrals close the shell; the umbonals open it; and the transmedians allow a sliding sideways movement of one valve across the other (see also p. 477).