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Show 1902.] PLECTOGXATHOUS FISHES. 291 vertebrae, not elongate, subequal in length except the three preceding the square hypural, which are extremely shortened. 3. L a c to ph r y s Swainson.- Body 3-sided ; carapace with three prominent ridges, a dorsal and two ventro-lateral. Vertebrae fourteen, the first eight elongate, the four preceding the oblong hypural shortened. In other characters like Ostracion. Division 2. G ymnodonte s . Supraclavicle oblique, sometimes nearly horizontal; lower three pterygials enlarged and immovably united to the coraco-scapular cartilage; upper pterygial small, suturally united to the scapula (see text-fig. 57). Anterior vertebra; with bifid divergent neural spines. Basis cranii simple. Suture between dentary and articu-lare evident. Pelvis absent. No spinous dorsal; no anal spines ; no ventrals; caudal rays, if present, ten to twelve in number. Three families : Tetrodontidae, Diodontidae, Molidae, I cannot find that the true interpretation of the bones of the pectoral arch in these fishes has been previously published. On a superficial examination there appears to be no scapula, and the pectoral fin to be supported by a series of four enlarged pterygials. In fact, the united upper pterygial and scapula together resemble one of the enlarged pterygials, both in size and shape, whilst the Text-fig. 57. Right half (inner side) of pectoral arches of (A) Diodon punctulatus and (B) Balistes verrucosus, scl., supraclavicle ; cl., clavicle; pci., postclavicle ; sc., scapula; cor., coracoid j ptr., pterygials. scapular foramen corresponds to one of the series of interspaces between them. The feature of the pterygials being immovably attached to the scapula and coracoid, either directly or synchon-drosially, is worth notice. The pectoral arch is so strikingly similar in all three families, that Siebenrock's suggestion that in Mola the bone which attaches the clavicle to the skull is the posttemporal, and not the supraclavicle as in Tetrodontidae, cannot be accepted. 19* |