Lying below it and parallel with it is the irregularly formed hypocoracoid. Attached to them is a row of bones, the actinosts, or pterygials, short, often hour-glass-shaped, which actually support the fin-rays. In the more specialized forms, or Teleosts, the actinosts are few (four to six) in number, but in the more primitive types, or Ganoids, they may remain numerous, a reminiscence of the condition seen in the Crossopterygians, and especially in _Polypterus_. Other variations may occur; the two coracoids sometimes are imperfect or specially modified, the upper sometimes without a foramen, and the actinosts may be distorted in form or position. [Illustration: FIG. 1.—Shoulder-girdle of a Flounder, _Paralichthys californicus_ (Ayres). ] =The Series Ganoidei.=—Among the lower _Actinopteri_ many archaic traits still persist, and in its earlier representatives the group approaches closely to the _Crossopterygii_, although no forms actually intermediate are known either living or fossil. The great group of _Actinopteri_ may be divided into two series or subclasses, the _Ganoidei_, or _Chrondrostei_, containing those forms, mostly extinct, which retain archaic traits of one sort or another, and the _Teleostei_, or bony fishes, in which most of the primitive characters have disappeared. Doubtless all of the _Teleostei_ are descended from a ganoid ancestry. Even among the _Ganoidei_, as the term is here restricted, there remains a very great variety of form and structure. The fossil and existing forms do not form continuous series, but represent the tips and remains of many diverging branches perhaps from some Crossopterygian central stock. The group constitutes at least three distinct orders and, as a whole, does not admit of perfect definition. In most but not all of the species the tail is distinctly and obviously heterocercal, the lack of symmetry of the tail in some Teleosts being confined to the bones and not evident without dissection. Most of the Ganoids have the skeleton still cartilaginous, and in some it remains in a very primitive condition. Usually the Ganoids have an armature of bony plates, diamond-shaped, with an enamel like that developed on the teeth. In all of them the pectoral fin has numerous basal bones or actinosts. All of them have the air-bladder highly developed, usually cellular and functional as a lung, but connecting with the dorsal side of the gullet, not with the ventral side as in the Dipnoans. In all living forms there is a more or less perfect optic chiasma. These ancient forms retain also the many valves of the arterial bulb and the spiral valve of the intestines found in the more archaic types of fishes. But traces of some or all of these structures are found in some bony fishes, and their presence in the Ganoids by no means justifies the union of the Ganoids with the sharks, Dipnoans, and Crossopterygians to form a great primary class, _Palæichthyes_, as proposed by Dr. Günther. Almost every form of