Page:Scientific results HMS Challenger vol 18 part 2.djvu/128

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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.

Definition.— 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.