The genus Pterocodon differs from the closely allied Pterocorys, its ancestral form, in the development of numerous solid feet around the terminal mouth, similar to the terminal corona of Calocyclas.
1. Pterocodon campana, Ehrenberg.
Pterocodon campana, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 10.
Pterocodon campana, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 82, Taf. xix. fig. 1.
Shell slender, campanulate, subconical, with two distinct strictures. Length of the three joints = 1 : 2 : 4, breadth = 2 : 3 : 5. Cephalis hemispherical, with a conical horn of twice the length. Thorax hemispherical, in the upper part with three divergent, conical horns, as long as the cephalis, and curved downwards. Abdomen with four transverse rows of large circular pores, increasing in size towards the mouth; the largest (undermost), five times as broad as the circular thoracic pores. Mouth not constricted, with a corona of twelve to fifteen divergent, conical feet.
Dimensions.—Length of the three joints, a 0.015, b 0.03, c 0.06; breadth, a 0.02, b 0.05, c 0.08.
Habitat.—Fossil in Barbados.
2. Pterocodon ornatus, n. sp. (Pl. [70], fig. 11).
Shell nearly ovate, with two deep strictures. Length of the three joints = 1 : 3 : 5, breadth = 1 : 5 : 7. Cephalis hemispherical, with a large oblique horn reaching half the length of the shell; three edges of the horn wing-shaped and dentated. Thorax hemispherical, in the middle zone with three conical wings, which are half as long as the thorax, and curved downwards. Pores hexagonal, roundish, twice as broad in the inflated abdomen as in the thorax. Mouth constricted, with a corona of from fifteen to eighteen conical, divergent, curved feet, similar to the thoracic wings.
Dimensions.—Length of the three joints, a 0.02, b 0.06, c 0.1; breadth, a 0.025, b 0.1, c 0.14.