Lithornithium dictyoceras, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1860, p. 840.
Shell with two distinct strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 5 : 6. Cephalis subspherical, with an oblique curved horn of the same length. Thorax conical, with three broad, triangular lattice-wings different in size and direction, two of which are directed outwards, the third downwards—each terminated by a strong spine. Abdomen oblique, inflated, with wide open, truncate mouth. On the shell surface some few conical spines are scattered. Pores irregular, roundish, of different sizes. On the peculiar symmetry of this remarkable form, compare the detailed description in my Monograph.
Dimensions.—Length of the three joints, a 0.02, b 0.06, c 0.08; breadth, a 0.02, b 0.1, c 0.12.
Habitat.—Mediterranean, Messina, surface.
Genus 586. Pteropilium,[[203]] Haeckel, 1881, Prodromus, p. 435.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three latticed free lateral wings on the sides of the thorax, prolonged into the horn of the cephalis in the form of three vertical, free cephalic wings.
The genus Pteropilium differs from the preceding closely allied Dictyoceras in the development of three free, vertical, latticed cephalic wings, expanded between the apical horn of the cephalis and the three wings of the thorax; they may be direct prolongations of the latter. Pteropilium, however, may also be derived directly from the Dicyrtida Callimitra or Clathrocorys by development of an abdomen. All these interesting forms are closely allied to the Plectoidea.
Subgenus 1. Clathropilium, Haeckel, 1881, Prodromus, p. 435.
Definition.—Thorax completely latticed, without three larger lateral holes between the three wings.
1. Pteropilium stratiotes, n. sp. (Pl. [70], figs. 9, 10).