Shell with twelve gates; the four lateral gates simple. Basal and mitral gates of about equal size. Shell similar to that of the preceding species, differing mainly in the different armature; the numerous spines, covering the convex outside of the four vertical rings, are not leaf-shaped, but conical, short, of very variable size, partly simple, partly irregularly branched. _Dimensions._--Length of the shell 0.08 (with spines 0.2), breadth 0.12. _Habitat._--South Pacific, Station 295, depth 1500 fathoms. {1004}Subgenus 2. _Tympanomma_, Haeckel. _Definition._--Shell with sixteen gates (eight median gates, paired on both sides of the sagittal ring, and eight lateral gates, paired on both sides of the frontal ring). The four lateral gates of the two preceding species (subgenus _Tympanura_) are bisected in _Tympanomma_ by the lateral parts of an incomplete equatorial ring. 3. _Tympanidium binoctonum_, n. sp. (Pl. 94, fig. 18). Shell with sixteen gates; the four lateral gates double, bisected by the lateral parts of an incomplete equatorial ring. Basal gates nearly rectangular, of the same breadth as the pentagonal mitral gates, but twice as long. Equatorial outline of the shell (seen in fig. 18 from the apical pole) octagonal. All rods of the shell thin, smooth. _Dimensions._--Transverse axis of the shell 0.1, sagittal axis 0.06. _Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms. 4. _Tympanidium barbadense_, Haeckel. "Hollow cylinder," &c., Bury, 1862, Polycystins of Barbados, pl. xvi. fig. 1. Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal gates kidney-shaped, of the same breadth as the circular mitral gates, but twice as long. Equatorial outline of the shell elliptical. All rods of the shell thin, smooth. _Dimensions._--Transverse axis of the shell 0.12, sagittal axis 0.08. _Habitat._--Fossil in South Naparima, Trinidad, Barbados. 5. _Tympanidium staurocircum_, n. sp. Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal and mitral gates of the shell of about equal size, roundish. Equatorial outline of the shell violin-shaped, with a sagittal constriction. All rods of the shell armed with short irregular spines. _Dimensions._--Transverse axis of the shell 0.12, sagittal axis 0.06. _Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms. Subfamily 2. PARATYMPANIDA, Haeckel, 1881, Prodromus, p. 447. _Definition._--#Tympanida# with two fenestrated horizontal rings, which are connected by a variable number of vertical rods or columellæ. The shell therefore becomes more completely latticed than in the other Tympanida, and approaches that of the #Spyroidea#. {1005}Genus 432. _Paratympanum_,[51] Haeckel, 1881, Prodromus, p. 447.