Page:Scientific results HMS Challenger vol 18 part 2.djvu/844

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Definition.— with the lateral margins of the valves dentate, without sagittal keel and without horns on the hinge.

The genus Conchellium and the four following genera represent together the subfamily Conchopsida, differing from the Conchasmida in the dentate lateral margins of the two valves. These are armed with a series of strong, conical teeth, and catch one into another just as the two valves of many Lamellibranchiata and Brachiopoda do (Pl. 124, figs. 1-16). Conchellium is the simplest form among the Conchopsida, since the valves are hemispherical, and possess neither a sagittal keel nor projecting horns.

1. Conchellium tridacna, n. sp. (Pl. 123, figs. 7, 7a).

Shell nearly spherical, finely tuberculated, the sagittal diameter somewhat longer than the two others. Borders of the two hemispherical valves smooth in 0.2 of the oral, and 0.1 at the aboral part, dentated in the remaining 0.7 part; on one side of each valve fourteen to sixteen very strong and long teeth, all nearly of the same size, about one-fourth as long as the shell-radius. In the half frontal perimeter of the shell (on one border of each valve) twenty-five to thirty pores, in the half sagittal perimeter thirty-five to forty, in the equator twenty-five to thirty. Pores circular, hexagonally framed, of equal size (except some smaller rows along the fissure), twice as broad as the bars. On the conical inside of each funnel-like pore six small spinules, between every three neighbouring pores a triangular facette (fig. 7a).

Dimensions.—Length of the shell 0.34 to 0.38, height 0.38 to 0.42, breadth 0.32 to 0.36.

Habitat.—North Pacific, Stations 250 to 253, depth 2740 to 3125 fathoms.

2. Conchellium hippopus, n. sp.

Shell nearly spherical, in the lateral perimeter (along the girdle-fissure) somewhat constricted. Borders of the two hemispherical valves semicircular, smooth in 0.3 of the oral, and 0.2 of the aboral part, dentated only in the remaining 0.5 middle part; on one side of each valve seven to eight very strong and long teeth, increasing in size towards the mouth, the longest (foremost) teeth nearly one-third as long as the shell-radius. In the half frontal perimeter of the shell (along one border of each valve) twenty-four to twenty-eight pores, in the half sagittal perimeter thirty-two to thirty-six, in the half equator twelve to fourteen. Pores circular, twice to three times as broad as the bars, smaller along the fissure.

Dimensions.—Length of the shell 0.06, height 0.065, breadth 0.055.

Habitat.—Central area of the Tropical Pacific, Station 274, depth 2750 fathoms.