Page:Scientific results HMS Challenger vol 18 part 1.djvu/606

398 Dimensions.—Length of the six-chambered internal cortical shell 0.25, of the outer 0.3; greatest breadth of the former 0.08, of the latter 0.12; pores of the proximal chambers of the inner shell 0.01, bars 0.005; pores of the distal chambers 0.003 to 0.005, square pores 0.02, bars 0.003; pores of the external cortical shell 0.002 to 0.006, bars 0.001.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

4. Desmocampe atractus, n. sp.

Inner cortical shell with six chambers of very different size and structure. Both proximal chambers kidney-shaped, with seven to eight transverse rows of subregular, roundish pores, twice to three times as broad as the bars. Both middle chambers cap-like, on the base with a circle of eight to ten very large square pores, on the distal cap with small irregular, roundish pores. Both distal chambers conical, also with small irregular, roundish pores. Outer cortical shell spindle-shaped, inflated in the equatorial zone, tapering conically towards both poles, with very delicate network of small roundish pores and thin bars. Surface covered with innumerable very small spines. Both medullary shells lenticular. (Resembles very much Peripanartus atractus, Pl. 40, fig. 7, but differs in the number of the chambers and their proportion to the outer mantle, which envelops spindle-like all six chambers.)

Dimensions.—Length of the six-chambered internal cortical shell 0.27, of the outer 0.32; greatest breadth of the former 0.09, of the latter 0.15; pores of the inner cortical shell (on an average)—proximal chambers 0.008, middle chambers 0.02, distal chambers 0.004, bars 0.004; pores of the outer cortical shell 0.002 to 0.004, bars 0.002.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

Definition.— with double cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus Desmartus differs from Desmocampe by the development of two hollow fenestrated tubes, opposite on both poles of the main axis, and bears therefore the same relation to it as Ommatartus to Ommatocampe. Both the former genera can be produced from the two latter by duplication of the cortical shell.

1. Desmartus larvalis, n. sp. (Pl. 40, fig. 12).

Zygartus larvalis, Haeckel, 1881, Prodromus et Atlas (pl. xl, fig. 12).

Inner cortical shell composed of six kidney-shaped chambers of nearly the same size and structure; every chamber twice as broad as long, with four to five transverse rows of irregular, roundish pores, twice to five times as broad as the bars; the basal pores of the distal chambers