. Bulletin - United States National Museum. Science. 166 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. While in the comatulids the radiating fiirruws and rid<res are always very distinct, in the closely allied pentacrinites they do not occur, and at most the joint face is indistinctly scalloped or beaded about the periphery. In the pentacrinites also the surface of the joint face, which in the comatulids is perfectly flat, is undulating. The joint faces of the syzygies in Atoj/ocrinus siboga are so extraordinary as to deserve special notice. Laterally and dorsally the central canal is bounded
. Bulletin - United States National Museum. Science. 166 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. While in the comatulids the radiating fiirruws and rid<res are always very distinct, in the closely allied pentacrinites they do not occur, and at most the joint face is indistinctly scalloped or beaded about the periphery. In the pentacrinites also the surface of the joint face, which in the comatulids is perfectly flat, is undulating. The joint faces of the syzygies in Atoj/ocrinus siboga are so extraordinary as to deserve special notice. Laterally and dorsally the central canal is bounded by a high ridge of moderate width; from this ridge there extends to the dorsal margin of the joint face in the dorsoventral line another ridge which at first is about as broad as the ridge from which it springs, but outwardly grad- ually broadens slightly; two similar ridges extend outward, one from either end of the laterodorsal ridge about the central canal, making with the median ridge an angle of about 45°, or about a right angle with each other. Just beyond these lateral ridges, entirely unconnected with the ridge about the central canal, separated from the lateral ridges by a ligament space about the same in shape and size as the two lateral ridges, are two more ridges, slightly broader than the others; each has a very narrow fan-shaped space beyond it. Beyond these two liga- ment spaces, the distal borders of which are approximately at right angles to the dorsoventral axis of the joint face, are two large obsolete muscular fos-sae, which are about as high as the distance between their proximal border and the dorsal edge of the joint face; these are rounded- triangular in shape; inwardly each rises somewhat, forming two parallel, very inconspicuous, low, and well rounded ridges, which are interiorly separated by a shallow rounded groove which becomes more accentuated just beyond the central canal, where it separates the inner ends of the inner pair of ridges; the inner
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