Page:Scientific results HMS Challenger vol 18 part 1.djvu/740

532 8. Hymeniastrum trigonarium, n. sp.

Arms one and a half times as long as broad, a little broader at the rounded end than at the base, with three strong conical radial spines, one larger (in the radius of each arm) and two smaller on both sides of this. Patagium complete, with four to five rectilinear parallel chamber-rows, enveloping the whole arms (with exception of the terminal spines) and forming a perfect equilateral triangle.

Dimensions.—Radius of the arms (without terminal spines) 0.18; breadth at the base 0.1, at the distal part 0.12.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Definition.— with three simple, undivided, chambered arms, connected by a patagium; triangular shell bilateral, one odd arm opposite to the odd angle between the two paired arms.

The genus Euchitonia, quite insufficiently characterised by Ehrenberg, was founded by him (1860) for one single species, afterwards (1872) described and figured as Euchitonia furcata. Retaining this species correctly as the type of this genus, I give to it here the above diagnosis. In my Monograph (1862, p. 503) I described seven Mediterranean species of Euchitonia. Three of these have in common the characters according to the present diagnosis: Euchitonia mülleri, Euchitonia virchowii, Euchitonia beckmanni; two others appertain (on account of the regular, not bilateral form) to Hymeniastrum, and two others (on account of the forked, not simple arms) to Trigonastrum. Afterwards (1880) three true fossil species of Euchitonia were described by Stöhr (Euchitonia cruciata, Euchitonia zittelii, and Euchitonia acuta). Some species of this genus are cosmopolitan, and appertain to the most common and everywhere represented.

Definition.—Arms with blunt ends, without terminal spines.

1. Euchitonia furcata, Ehrenberg.

Euchitonia furcata, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 308; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. vi. iii. fig. 6.

Distance between the paired arms about half as large as their distance from the odd arm. All three arms nearly of the same size and form, about twice as long as broad, one and a half times at the