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.
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.