The genus Eucyrtidium (as here stated in the definition) and the three following nearly allied genera differ from the preceding Stichocorida in the more or less constricted mouth, and the consequent ovate or spindle-form of the multiarticulate shell. The middle joints of the latter are broader than the upper and the lower joints. In the earlier definition given in my Monograph (1862, pp. 312 to 320), the genus had a much wider sense; but the very large number of species since detected requires a more strict definition. Ehrenberg confounded in his genus Eucyrtidium a large number of very different Cyrtoidea. In his last works (1872, 1875) he described not less than one hundred and eleven species, fifty-five fossil and fifty-six living (eight fossil species being yet living). But, in reality, these one hundred and three species belong to twenty or twenty-two very different genera of Cyrtoidea.
Subgenus 1. Eucyrtis, Haeckel, 1881, Prodromus, p. 438.
Definition.—All joints of the shell nearly of the same length (excepting often the first). Surface smooth or rough, without spines.
1. Eucyrtidium acuminatum, Ehrenberg.
Eucyrtidium acuminatum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 104, Taf. iv. fig. 6.
Eucyrtidium acuminatum, Haeckel, 1862, Monogr. d. Radiol., p. 326.
Lithocampe acuminata, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 84.Shell smooth, slender, nearly spindle-shaped, without external strictures, but with eight to nine internal septal rings. All joints (except the first) nearly of the same length (or the upper somewhat longer). The fifth joint is the broadest. Cephalis small, subspherical, with a short, conical horn. Pores very small and numerous, regular, hexagonal, four to six on the length of each joint.
Dimensions.—Length of the shell (with eight joints) 0.14; length of each joint about 0.02; greatest breadth, in the fifth joint, 0.07.
Habitat.—Fossil in Tertiary rocks of Sicily (Caltanisetta, Grotte, &c.).
2. Eucyrtidium tropezianum, Haeckel.
Shell smooth, slender, nearly spindle-shaped, without external strictures, but with seven or eight internal septal rings. All joints of the same length. The fifth and sixth joints are the broadest. Cephalis hemispherical, with a pyramidal horn of the same length. Pores very small and numerous, regular, circular, hexagonally framed, five to six in the length of each joint. (Very near to the preceding species, but more regular, and with different pores.)
