_Acanthometra arachnoides_, Claparède, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 675. Spines straight, cylindrical, divided into three divergent straight branches of equal size; each branch two to three times as long as the simple thicker basal part. _Dimensions._--Length of the spines 0.12 to 0.2 of the branches 0.08 to 0.14. _Habitat._--North Atlantic, coast of Norway, Claparède, surface. 2. _Plagiacantha furcata_, n. sp. Spines straight, cylindrical, divided into two divergent straight branches of equal size, of about the same length as the simple basal part. The spines and their branches are smooth. _Dimensions._--Length of the spines 0.24, of their fork-branches 0.12. _Habitat._--North Pacific, Station 254, surface. 3. _Plagiacantha dodecantha_, n. sp. Spines straight, three-sided prismatic, in the middle with one verticil composed of three divergent straight branches of equal size, of about the same length as the simple basal part. The edges of the spines and their branches are thorny. _Dimensions._--Length of the spines 0.24, of the branches 0.1. _Habitat._--Central Pacific, Station 274, surface. 4. _Plagiacantha abietina_, Richard Hertwig. _Plagiacantha abietina_, Richard Hertwig, 1879, Organismus d. Radiol., p. 72, Taf. vii. figs. 6-6_b_. Spines straight, three-sided prismatic, with three verticils of three divergent straight lateral branches, decreasing in size towards the distal end; the branches of the first verticil about twice as long as those of the second, and four times as long as those of the third verticil. All nine branches of each spine simple, straight, three-sided pyramidal. _Dimensions._--Length of the spines 0.2 to 0.3, of the basal branches 0.06 to 0.08. _Habitat._--Mediterranean, Messina (R. Hertwig), surface. 5. _Plagiacantha verticillata_, n. sp. Spines curved, three-sided prismatic, with six to nine verticils of three divergent branches, decreasing in size towards the distal end; the branches of the first verticil about twice as long as those of the fourth verticil. All branches simple, slightly curved, bristle-shaped. _Dimensions._--Length of the spines 0.27, of the basal branches 0.12. _Habitat._--South Pacific, Station 296, surface. {911}6. _Plagiacantha elatine_, n. sp. Spines straight, three-sided prismatic, with prominent wing-like edges and ten to twelve verticils of three divergent branches, decreasing in size towards the distal end; the branches of the three or four basal verticils are again ramified and much larger than the simple branches of the distal verticils. _Dimensions._--Length of the spines 0.36, of the basal branches 0.14. _Habitat._--Central Pacific, Station 268, depth 2900 fathoms. Subfamily 2. TETRAPLAGIDA, Haeckel, 1881, Prodromus, p. 424. _Definition._--#Plagonida# with four radial spines. Genus 386. _Tetraplagia_,[5] Haeckel, 1881, Prodromus, p. 424.