OCR Text |
Show 1902.] PLECTOGNATHOUS f is h e s . 287 Spinous dorsal, if present, of few rays ; no anal spines; ventrals, if present, each represented by a spine (rarely with the addition of one or two rudimentary soft rays). Caudal rays in small number, ten to eighteen. Four families : Triacanthidse, Triodontidse, Balistidse, and Ostraciontidse. In the fishes of this division the pectoral arch is very similar to that of the Acanthuridse, except that the post-temporal is completely united suturally to the squamosal. The vertebral column also is like that of Perciform fishes ; and although Dareste has ascribed to Triodon diapophyses on the posterior prsecaudal and most of the caudal vertebrse, it is evident, from studying his figure and comparing with skeletons of Triacanthus and Balistes, that he is referring to the prsezygapophyses, which are somewhat enlarged in this region in all these fishes. Family 1. T riacanthid^e . Prsecaudal vertebrae with parapophyses from the third or fourth to the last; epipleurals present. Prseorbital not ossified ; ethmoid region high, a large nasal cavity bounded by ethmoid and prae-frontal; palatine arch firmly united to the skull; premaxillaries protractile, free from the maxillaries; teeth in the jaws separate, conical or incisor-like ; palate toothless ; fourth upper pharyngeals toothed ; lower pharyngeals separate; opercular bones reduced, but with their normal relations. Pelvis present, firmly united to the pectoral arch. Two nostrils on each side. Four gills, a slit behind the fourth ; pseudobranchise present; six branchiostegals. Scales small, sometimes spinate or osseous. Spinous dorsal with two to six spines; soft dorsal and anal of moderate length or rather short; ventrals each represented by a strong spine, with an inner basal knob which locks it when everted, rarely with the addition of one or two rudimentary soft rays. Air-bladder present. Genera. 1. T riacanthus 1 Cuv.- Body compressed, caudal peduncle long and slender. Scales small, rough. Lateral line present. D. IV -V , 22-25 ; A. 16-20. Ventrals without soft rays. Caudal forked, with 12 rays. A series of incisors in each jaw, with a few inner rounded teeth. Twenty vertebrae. 2. T riacanthodes 2 Bleeker. - Body compressed, caudal peduncle short. Scales small, juxtaposed. No distinct lateral 1 The Oligocene genus Acanthopleurus Agassiz has a rounded caudal, but in other respects seems scarcely different from Triacanthus. 2 Spinacantkus Agassiz, from the Eocene of Monte JtSolca, may belong to this family. It resembles Triacanthodes in its dorsal, anal, and caudal fins, except that the six dorsal spines are very long and strong. The eye is placed high, below the first dorsal spine, and the teeth are stout and conical. The pelvis and ventral fins were apparently not strongly developed, and Gill considers this fish to be the type of a separate family. |