. Outlines of zoology. orms with pectoral fins obtusely lobate and uniserial oracutely lobate and biserial; with scales and dermal skull bones oftencovered with enamel-like ganoin ; with a pair of jugular plates betweenthe rami of the lower jaw. All are extinct except Polypterus andCalamoichthys from African rivers. Examples, Osteolepis (LowerDevonian), Holoptychius (Devonian), Megalichthys (Carboniferous), In Polypterus, the body is covered with rhombic ganoid scales;there are numerous dorsal fins; the tail is diphycercal; the pectoralfin has three basal pieces as in Elasmobranchs, then two r
. Outlines of zoology. orms with pectoral fins obtusely lobate and uniserial oracutely lobate and biserial; with scales and dermal skull bones oftencovered with enamel-like ganoin ; with a pair of jugular plates betweenthe rami of the lower jaw. All are extinct except Polypterus andCalamoichthys from African rivers. Examples, Osteolepis (LowerDevonian), Holoptychius (Devonian), Megalichthys (Carboniferous), In Polypterus, the body is covered with rhombic ganoid scales;there are numerous dorsal fins; the tail is diphycercal; the pectoralfin has three basal pieces as in Elasmobranchs, then two rows ofradials, and then the dermal fin-rays or dermotrichia; the air-bladderis double and is used in respiration, its duct opens ventrally into thepharynx; the young form has an external gill on the operculum; the 570 PISCES—FISHES. oral part of the hypophysis retains its opening into the mouth. Thegenus Calamoichthys has very similar characters, but no pelvic two forms may almost be called living Fig. 304.—Larva of Polypterus (after Budgett), iJ inch in length. , Large external gill of the hyoid arch; Pc., pectoral fins; Pv., pelvicfins. The larva is drawn in a very characteristic attitude. The following three orders are often grouped as Actino-pterygii, with the following characters. The paired fins arenever lobate, they have short basal pieces, and are mainlysupported by dermal fin-rays. Order 2. Chondrostei—with cartilaginousinternal skeleton Living examples:—Sturgeon (Acipenser), Polyodon, Sca-phirhynchus.
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
