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Show 1902.J PLECTOGXATHOUS FISHES. 297 rough or tessellated. Body truncate posteriorly, without caudal peduncle. Caudal fin absent, the dorsal and anal fins confluent posteriorly. Skeleton moderately ossified. Air-bladder absent. Genera. 1. M o la C u v .-Body ovate, compressed ; skin thick, rough. Vertebrae 17. 2. R a x z a x ia Nardo.-Seems chiefly different from Mola in having the body covered with small hexagonal juxtaposed plates. P ar t II. Notes on some Plectognathous Fishes, and Descriptions o f some new species in the British Museum Collection. In these descriptions the length of head is measured from the tip of the snout to the upper end of the gill-opening, the depth of body at the level of the vent, the movable pelvis or inflatable belly making the measurement of the greatest depth uncertain. B a l istes n a u f r a g ium Jordan & Starks. In descriptions of this species a feature of some importance has been overlooked, i. e. that the scales on the cheeks are arranged in parallel horizontal series, with naked lines intervening between those in front of the pectoral, and although closely allied to Balistes capriscus Linn, it is still closer to B. flavimarginatus Rupp., and should have been placed in the genus Xanthichthys recognized by the authors who named it. Incidentally this species demonstrates of what little value are genera based on features so trivial as those supposed to separate Balistes from Xanthichthys. B a l iste s c a s t a x e u s Richardson. This species, described by Richardson in the ‘ Voyage of the Sulphur, Fishes' (p. 126, pi. 59), has been included by Giinther in the synonymy of Balistes capriscus Linn., from which it differs in many ways, and I therefore take the opportunity of redescribing Richardson's type specimen. Depth of body twice in total length, length of head 3 times. Snout 3 times as long as the eye-diameter, which is f of the interorbital width, which is less than ^ the length of head and equal to the length of the gill-opening. A groove below the nostrils; 2 or 3 enlarged plates behind the gill-opening. D. I ll, 28. A. 26. The first dorsal spine above the gill-opening, with about 8 vertical rows of minute tubercles anteriorly, somewhat curved, its length I f times in the length of head; second and third spines prominent; soft dorsal somewhat elevated anteriorly, the fifth ray the longest, longer than the first dorsal spine. Anal similar, but not so deep. Caudal truncate, with the outer rays slightly produced. Scales on the cheeks in oblique series without naked lines intervening, on the caudal peduncle not bearing |