AMERICAN JOURNAL MATERIALS TOWARD A MONOGRAPH OF THE GADINIIDiB. BY W. H. BALL, SMITHSONIAN INSTITUTION. The genus Cradinia was instituted by Gray in 1824, for the Patella afra of Gmelin. In 1840 he instituted for it a special family. In his early publications on the subject, he rightly placed it near Siplionaria in his classification. Afterwards, mis-led by the erroneous description of Philippi, he referred it to the Cervicohranchiata, with Tectura and Scurria which have the gills over the neck, and Lepeta which has no gills. Most other authors have followed Gray. The Messrs. Adams combine in the sub-order EdriojotJialma the Chitonidce, the Dentaludce, Fissurellidce, Tecturidce, Lepet-idce and G-adiniidce, thus reaching a climax of confusion rarely equalled. Chenu, as usual, follows the Messrs. Adams, but unites a fossil genus (whose affinities are clearly with Eynai'gin-tda, etc.) with Gadinia in the Gadiniidce. Keferstein, with a singular misapprehension of its affinities, places Gadinia in the Acmoeidce and refers it to the Tcenioglossa. A more thorough examination of the soft parts than that afforded by the single specimen of Dr. Philippi, shows that the first conclusion of Dr. Gray was much nearer the truth than any subsequent references. It is a true pulmonate, breathing air by means of a lung and unprovided with gills of any kind. The anatomy shows affinities with the Auriculidce, and the dentition has relations with that family, but more strongly with that of the Siphonariidoe. Order PULMONATA. Sub-order BASSOMATOPHORA. Family GADINIID^, Gray. Genus GADINIA. Syn. Gadinia, Gray, Tilloch's (London) Philos. Mag. Ixiii, 1824, pp. 214—271. Isis, von Oken, Heft v, col. 460, 1834. Mouretia] Sby. (nee Gray), Proc. Zool. Soc. 1835, p. 6.