T he pretty little fish discovered by the Rev. P. B. Brodie in the Keuper beds of Rowington, and submitted to me for description, belongs undoubtedly to the genus Palæoniscus . The extremities are unfortunately deficient, but enough of the tail remains to show that it was completely heterocerque. The specimen (Pl. XI. figs. 1 & 2) measures one inch and three-quarters in length, by six-tenths of an inch at its greatest depth. The pectoral fins are lost, together with the head and the scapulo-coracoid arch. The other locomotive organs are well preserved, with the exception of the extremity of the caudal fin. The ventral fins occupy a very advanced position in front of the middle line of the body. They are small, and contain few fin-rays, but the anterior edge is bordered with fulcral scales of considerable thickness.The anal fin is situated near the hinder extremity of the body. Ten rays are seen in the specimen (fig. 3), of which the three first are short, pointed, and undivided. The remainder have transverse articulations at distant intervals, and dichotomize towards their extremities. The hinder portion of the fin is deficient. The dorsal fin is placed immediately above the anal fin. I t contains about a dozen rays. Of these the fulcral rays arc more numerous and more elongated than those in advance of the anal fin. In other respects the two fins are very similar. The portion of the tail which is preserved, shows the scales of the dorsal ridge elongating gradually