The pelvis, remote from the head, is formed, in the shark, of a single or paired cartilage with smaller elements at the base of the fin-rays. In the males a cartilaginous generative organ, known as the clasper, is attached to the pelvis and the ventral fins. In the Elasmobranchs the tail vertebræ are progressively smaller backward. If a caudal fin is present, the last vertebræ are directed upward (_heterocercal_) and the greater part of the fin is below the axis. In other forms (sting-rays) the tail degenerates into a whip-like organ (_leptocercal_), often without fins. In certain primitive sharks (Ichthyotomi), as well as in the Dipnoi and Crossopterygii, the tail is _diphycercal_, the vertebræ growing progressively smaller backward and not bent upward toward the tip. In the chimæras (_Holocephali_) the notochord persists and is surrounded by a series of calcified rings. The palate with the suspensorium is coalesced with the skull, and the teeth are grown together into bony plates. [Illustration: FIG. 48.--Shoulder-girdle of a Toadfish, _Batrachoides pacifici_ (Günther).] [Illustration: FIG. 49.--Shoulder-girdle of a Garfish, _Tylosurus fodiator_ (Jordan and Gilbert).] =The Archipterygium.=--The Dipnoans, Crossopterygians, and Ganoids represent various phases of transition from the ancient cartilaginous types to the modern bony fishes. In the Ichthyotomous sharks, Dipnoans, and Crossopterygians the segments of the pectoral limb are arranged axially, or one beyond another. This type of fin has been called _archipterygium_ by Gegenbaur, on the theory that it represents the condition shown on the first appearance of the pectoral fin. This theory is now seriously questioned, but it will be convenient to retain the name for the pectoral fin with segmented axis fringed on one or both sides by soft rays. [Illustration: FIG. 50.--Shoulder-girdle of a Hake, _Merluccius productus_ (Ayres).] The archipterygium of the Dipnoan genus _Neoceratodus_ is thus described by Dr. Günther ("Guide to the Study of Fishes," p. 73): "The pectoral limb is covered with small scales along the middle from the root to the extremity, and is surrounded by a rayed fringe similar to the rays of the vertical fins. A muscle split into numerous fascicles extends all the length of the fin, which is flexible in every part and in every direction. The cartilaginous framework supporting it is joined to the scapular arch by a broad basal cartilage, generally single, sometimes showing traces of a triple division. Along the middle of the fin runs a jointed axis gradually becoming smaller and thinner towards the extremity. Each joint bears on each side a three-, two-, or one-jointed branch."