The genus Eucoronis and the following two nearly allied genera (Plectocoronis and Podocoronis) compose together the important subfamily Eucoronida. In this typical main group of Coronida the shell is constantly composed of three rings and six gates. The vertical sagittal ring and the horizontal basal ring are complete (as in the Semantida); the vertical frontal ring is incomplete. Between these three rings remain six large open gates, the four upper (or lateral) are always much larger than the four lower (or basal gates). Eucoronis may be derived from Semantis by development of the frontal ring.
Subgenus 1. Acrocoronis, Haeckel, 1881, Prodromus, p. 445.
Definition.—Rings smooth or rough, armed with numerous short spines or thorns.
1. Eucoronis perspicillum, n. sp. (Pl. 82, fig. 6).
Frontal ring elliptical, twice as broad as high, with a slight constriction at the apical pole, armed with three pairs of short conical spines, one apical pair (near the constriction) and two lateral pairs (one upper and one lower pair). Sagittal ring of the same height, half the breadth and double the thickness, also armed with three pairs of spines (one basal, one dorsal, and one ventral pair).
Dimensions.—Height of the frontal ring 0.11, breadth 0.22.
Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.
2. Eucoronis lævigata, n. sp.
Frontal ring elliptical, smooth, one and a half times as broad as high, without sagittal constriction, with horizontal basal gates. Sagittal ring of the same height and thickness, also elliptical and smooth. No spines on either of the smooth rings.
Dimensions.—Height of the frontal ring 0.1, breadth 0.15.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
3. Eucoronis nephrospyris, n. sp. (Pl. 82, fig. 5).
Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with a sagittal constriction (often much deeper than in the specimen figured). Sagittal ring ovate, about two-thirds as high as the frontal ring. Rods of both rings without edges, cylindrical, armed with numerous short conical thorns.
Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.15 to 0.18.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface and at various depths.
