In some fish beak-like structures occur, formed partly of teeth, partly of the underlying jaw bones. These beaks are of two kinds: (1) In _Scarus_, the parrot fish, the premaxillae and dentaries bear numerous small, separately developed teeth, which are closely packed together and attached by their proximal ends to the bone, while their distal ends form a mosaic. Not only the teeth but the jaws which bear them are gradually worn away at the margins, while both grow continuously along their attached edge. (2) In Gymnodonts, e.g. _Diodon_, the beaks are formed by the coalescence of broad calcified horizontal plates, which when young are free and separated from one another by a considerable interval. In some Teleosteans the differentiation of the teeth into biting teeth and crushing teeth is as complete as in _Lepidosteus_. Thus in the Wrasse (_Labrus_), the jaws bear conical slightly recurved teeth arranged in one or two rows, with some of the anterior ones much larger than the rest. The bones of the palate are toothless, while both upper and lower pharyngeal bones are paved with knob-like crushing teeth; such pharyngeal teeth occur also in the Carp but are attached only to the lower pharyngeal bone, the jaw bones proper being toothless. In DIPNOI the arrangement of the teeth is very similar to that in Holocephali. The mandible bears a single pair of grinding teeth attached to the splenials, and a corresponding pair occur on the palato-pterygoids. In front of these there are a pair of small conical vomerine teeth loosely attached to the ethmoid cartilage. The palato-pterygoid teeth of _Ceratodus_ are roughly semicircular in shape with a smooth convex inner border, and an outer border bearing a number of strongly marked ridges. The teeth of the extinct Dipteridae resemble those of _Ceratodus_ but are more complicated. ENDOSKELETON. SPINAL COLUMN[41]. The spinal column of fishes is divisible into only two regions, a caudal region in which the haemal arches or ribs meet one another ventrally, and a precaudal region in which they do not meet. The various modifications of the spinal column in fishes can be best understood by comparing them with the arrangement in the simplest type known, namely _Amphioxus_. In _Amphioxus_ the notochord is immediately surrounded by a structureless cuticular layer, the _chordal sheath_. Outside this is the _skeletogenous layer_, which in addition to surrounding the notochord and chordal sheath embraces the nerve cord dorsally, and laterally sends out septa forming the _myomeres_.