Genus 440. _Eutympanium_,[58] Haeckel, 1881, Prodromus, p. 447. _Definition._--#Tympanida# with two simple equal horizontal rings, connected by numerous (six to eight or more) parallel and vertical columellæ. The genus _Eutympanium_ contains those Tympanida in which the drum-shaped shell is composed of two simple, parallel and equal horizontal rings, and numerous vertical and parallel rods or columellæ connecting them. The number of the latter is at least six or eight. Two opposite of these must be regarded as remaining vertical parts of the sagittal ring, two others as parts of the frontal ring, whilst the other columellæ (between the former and the latter) are secondary and intercalated. Therefore _Eutympanium_ may be derived from _Tympanidium_ by reduction and loss of the apical and basal parts of the sagittal ring. 1. _Eutympanium musicantum_, n. sp. (Pl. 83, fig. 2). Eight parallel and vertical columellæ, simple, straight and smooth. Both horizontal rings equal, circular, each armed with eight to twelve short conical thorns. _Dimensions._--Height of the shell 0.09, breadth 0.07. _Habitat._--Central Pacific, Station 266, depth 2750 fathoms. {1014}2. _Eutympanium octonarium_, n. sp. Eight vertical columellæ slightly curved, thorny. Both horizontal rings equal, octagonal, each armed with eight large, irregularly-branched spines, which on the mitral ring are directed obliquely upwards, on the basal ring downwards. _Dimensions._--Height of the shell 0.12, breadth 0.1. _Habitat._--Central Pacific, Station 268, depth 2900 fathoms. 3. _Eutympanium coronarium_, n. sp. Eight thorny columellæ, obliquely descending and curved like a bow, divergent in the upper part, convergent in the lower. Basal ring circular, mitral ring octagonal. Both horizontal rings armed with eight stout thorny spines, which on the mitral ring are smaller and directed obliquely upwards, on the basal ring larger and directed downwards, each with a recurved hook. _Dimensions._--Height of the shell 0.08, breadth 0.06. _Habitat._--South Atlantic, Station 332, depth 2200 fathoms. 4. _Eutympanium militare_, n. sp. (Pl. 82, fig. 11). Ten parallel and vertical columellæ straight and smooth, cylindrical. Both horizontal rings equal, circular, armed with numerous short conical spines, divergent in all directions. Ten to twenty spines on each ring larger than the others. _Dimensions._--Height of the shell 0.1, breadth, 0.08. _Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms. 5. _Eutympanium dodecarium_, n. sp. Twelve vertical columellæ, slightly curved, smooth. Mitral and basal rings circular, both horizontal rings armed with twelve stout, irregularly-branched spines, which are prolongations of the columellæ, and on the mitral ring directed upwards, on the basal ring downwards. _Dimensions._--Height of the shell 0.13, breadth 0.1. _Habitat._--South Pacific, Station 300, depth 1375 fathoms. {1015}----