Definition.—Podocyrtida with the basal mouth of the shell fenestrated (vel Tricyrtida triradiata clausa).
Genus 595. Lithornithium,[[212]] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.
Definition.—Theoperida (vel Tricyrtida triradiata clausa) with three solid lateral wings on the thorax.
The genus Lithornithium has an ovate or spindle-shaped shell, with two distinct strictures, and tapering towards both poles. The abdomen is simple, whilst the cephalis bears an apical horn, and the thorax three free, lateral, solid, divergent wings. It may be derived from Pterocorys by development of a terminal lattice-plate closing the mouth.
1. Lithornithium ciconia, n. sp. (Pl. [67], fig. 3).
Shell nearly spindle-shaped, with two indistinct strictures. Length of the three joints = 1 : 2 : 4, breadth = 1 : 3 : 3. Cephalis ovate, with a large pyramidal spine of twice the length. Thorax three-sided pyramidal with three pyramidal wings of the same length, the broad triangular bases of which occupy the whole length of the thoracic edges. Abdomen inversely ovate (in the figured specimen broken off, in another specimen, found afterwards, completely closed at the distal end). Pores very small, regular, circular, of equal size.
Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.08; breadth, a 0.02, b 0.06, c 0.06.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
2. Lithornithium falco, n. sp. (Pl. [67], fig. 1).
Shell nearly ovate, with two sharp strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 4 : 3. Cephalis hemispherical, with a conical spine of the same length. Thorax subspherical, with three conical wings of half the length, little curved, arising with broad triangular base from the upper half of the thorax. Abdomen inversely conical. Pores irregular, roundish, of different sizes.