The genus Lithocampe is the oldest of all "Polycystina," being founded by Ehrenberg in 1838 upon Lithocampe radicula. Afterwards numerous other species, which belong to very different genera, were described by him. In 1862 I attempted to give a more strict definition of this genus in my Monograph (p. 312 to 315), and separated it from the closely allied and often confounded Eucyrtidium by the absence of a cephalic horn. The great number of species afterwards discovered leads to the stricter definition given above.
Subgenus 1. Lithocampula, Haeckel.
Definition.—All joints of the shell (except often the first) are equal or nearly equal in length.
1. Lithocampe eupora, Haeckel.
Shell smooth, ovate or subconical, with three deep strictures. Four joints equal in length, gradually increasing in breadth, each with three transverse rows of regular, circular, hexagonally-framed pores; the fourth joint is the broadest. Mouth little constricted, of the same breadth as the third joint.
Dimensions.—Length of the shell (with four joints) 0.08; length of each joint 0.02, greatest breadth 0.06.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms; North Atlantic, depth 3600 fathoms (Morse).
2. Lithocampe platycephala, Haeckel.
Shell smooth, subconical or slenderly ovate, with three slight strictures. Four joints equal in length, slightly increasing in breadth towards the mouth. The hemispherical cephalis with longitudinal ribs and irregular pores, each of the three other joints with four transverse rows of regular, circular pores. Mouth strongly constricted, half as broad as the third and fourth joints.
Dimensions.—Length of the shell (with four joints) 0.12; length of each joint 0.03, greatest breadth 0.06.
Habitat.—North Atlantic, depth 3600 fathoms (Morse).
3. Lithocampe nereidum, Haeckel.
Shell smooth, slenderly ovate, with four deep strictures. Five joints equal in length, the fourth being the broadest. Each joint with three transverse rows of small, regular, circular pores
