been termed _Sparoid_ scales; but their distinction from ctenoid scales is by no means sharp, and there are even intermediate forms between the cycloid and ctenoid types. Both kinds of scales may occur not only in species of the same genus of fishes, but in the same fish. [Illustration: Fig. 12.--Ctenoid scale of Scatophagus multifasciatus (magn.)] [Illustration: Fig. 13.--Ctenoid scale of Platycephalus cirrhonasus (magn.)] [Illustration: Fig. 14.--Ctenoid scale of Gobius ommaturus (magn.)] [Illustration: Fig. 15.--Ctenoid scale of Lethrinus (magn.)] [Illustration: Fig. 16. Ganoid Scales.] _Ganoid_ scales are hard and bony, covered with a layer of enamel; they are generally rhombic or quadrangular, rarely rounded and imbricate; and arranged in oblique rows, those of one row being linked together by an articulary process. This type of scales, common in fossil Ganoid fishes, occurs among recent fishes in _Lepidosteus_ and _Polypterus_ only. Finally, in Sharks, the Balistidæ, and others, true scales are absent and replaced by the ossified papillæ of the cutis, which give the surface the appearance of fine-grained chagreen. These generally small bodies, as well as the large osseous scutes of the Rays, Sturgeons, etc., have been comprised under the common name _Placoid_ scales; a term which deservedly is being abandoned. [Illustration: Fig. 17.--Dermal papillæ of Monacanthus trossulus.] [Illustration: Fig. 18.--Dermal papillæ of Monacanthus hippocrepis (magn.)] [Illustration: Fig. 19.--Cycloid scale from the lateral line of Odax lineatus (magn.)]