It may be derived from Theoconus by increase in the number of the joints. Some species are distinguished by a curved axis, which gives them a horn-like appearance; these may be separated as a peculiar genus, Cornustrobus.
Subgenus 1. Conostrobus, Haeckel.
Definition.—Shell regularly conical, with straight axis; all joints nearly equal in length, gradually increasing in breadth.
1. Lithostrobus monostichus, n. sp.
Shell slenderly conical, smooth, with straight axis, and eight to ten deep strictures. All joints nearly of the same length, gradually increasing in breadth; the eighth joint twice as broad as the fourth. In each joint only a single transverse series of small, circular, regular pores. Horn of the cephalis conical, straight, of twice the length. (Similar to Lithostrobus tetrastichus, Pl. 80, fig. 6, but in each joint there is only a single series of pores.)
Dimensions.—Length of the shell (with ten joints) 0.2, of each joint 0.02; breadth of the fourth joint 0.03, of the eight 0.06.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
2. Lithostrobus distichus, n. sp.
Shell conical, papillate, with straight axis, and four to six deep strictures. All joints nearly of the same length, the fifth twice as broad as the second. In each joint two transverse rows of large, circular pores. Horn of the cephalis stout, straight, conical, of the same length.
Dimensions.—Length of the shell (with six joints) 0.18, of each joint 0.03; breadth of the second joint 0.04, of the fifth 0.08.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
3. Lithostrobus tristichus, Haeckel.
Shell slenderly conical, smooth, with straight axis, and eight to ten deep strictures. All joints nearly of the same length, the eighth joint twice as broad as the third. In each joint three transverse rows of pores. Horn of the cephalis bristle-shaped, strongly curved, about as long as the shell (Ehrenberg confounds this species with Lithostrobus cuspidatus).
Dimensions.—Length of the shell (with eight joints) 0.16, of each joint 0.02; breadth of the fourth joint 0.04, of the eighth 0.08.
Habitat.—North Pacific, Kamtschatka (Bailey); Station 241, depth 2300 fathoms.
