Frontal ring kidney-shaped, one and a half times as broad as high, with a slight sagittal constriction. Sagittal ring ovate, smaller, about of the same size as the elliptical basal ring. Rods of all three rings cylindrical, bearing numerous short and stout curved spines, partly simple, partly branched. Four bunches of larger spines on the four corners of the basal ring, and one very large bunch on the apical pole. Basal gate elliptical, one and a half times as broad as long. _Dimensions._--Height of the frontal ring 0.13, breadth 0.18. _Habitat._--Indian Ocean (Madagascar), Rabbe, surface. 3. _Coronidium cervicorne_, n. sp. (Pl. 82, fig. 1). Frontal ring kidney-shaped, twice as broad as high, one and a half times as broad as the elliptical basal ring, both with a slight sagittal constriction. Sagittal ring ovate. All three rings {975}(in the figure seen from the apical pole) with cylindrical rods, armed with numerous stout spines, branched like a deer's antler. Basal gate rather oblong, twice as broad as long. _Dimensions._--Height of the frontal ring 0.08, breadth 0.16. _Habitat._--Central Pacific, Station 272, depth 2600 fathoms. 4. _Coronidium acacia_, n. sp. (Pl. 82, fig. 2). Frontal ring and sagittal ring nearly circular, of equal size, truncated at the base. Basal ring circular, somewhat smaller. All three rings with prominent edges, bearing bunches of short and straight pointed spines, like those of an Acacia. Basal gate circular. _Dimensions._--Height of the frontal ring 0.12, breadth 0.14. _Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms. Genus 417. _Acanthodesmia_,[36] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 485. _Definition._--#Coronida# with five large, partly latticed gates (four lateral and one basal). Skeleton composed of two incomplete, partly fenestrated meridional rings, and one complete basal ring. The genus _Acanthodesmia_, the oldest known form of all Coronida, differs from the preceding _Coronidium_, its ancestral form, in the development of irregular loose lattice-work along the rings, and therefore bears to it the same relation that _Zygostephanium_ does to _Zygostephanus_. The first species described by Johannes Müller, _Acanthodesmia vinculata_ ("with five large gates between the bars of the shell") remains the true type of this genus; the second species described by him (_Acanthodesmia dumetum_) belongs to the Plectanida (_Polyplecta_). 1. _Acanthodesmia vinculata_, J. Müller. _Acanthodesmia vinculata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. figs. 4-6 (_non_ 7). _Lithocircus vinculatus_, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.