. Bulletin - United States National Museum. Science. 188 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. narrow triangle, extends from a bnse coinciding with the inner side of the joint face to an attenuated point at the outer distal angle. The greater part of the outer half of the joint face beyond the central canal is occupied by an unpaired interarticular ligament fossa. The articulation between the first and second segments of the distal pinnules: This is essentially the same as the corresponding articidation in P^. The articulation between the sixth and seventh segment of the distal pinnules:
. Bulletin - United States National Museum. Science. 188 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. narrow triangle, extends from a bnse coinciding with the inner side of the joint face to an attenuated point at the outer distal angle. The greater part of the outer half of the joint face beyond the central canal is occupied by an unpaired interarticular ligament fossa. The articulation between the first and second segments of the distal pinnules: This is essentially the same as the corresponding articidation in P^. The articulation between the sixth and seventh segment of the distal pinnules: The dorsal border of the joint face is eventy convex; the ventral border is con- cave; the two ventral angles are well rounded. There is the usual liroad median fulcral ridge. Occupying two pumpkin-seed shaped areas, of which the rounded ends coincide with the rounded ventrolateral angles of the joint face and the sides converge inwardly to a point a little more than half way to the median line and slightly beyond tlie level of the central canal, are two large and deep muscular fossse lodging a con- spicuous pair of muscle bundles. Similar paired muscle bundles appear to oc- cur at all of the articulations of the distal pin- nules beyond that between the first two ARTICULATIONS OF THE CIRRI. The articulation between the first cirrus seg- ment and the centrodorsal is usually plane, but the periphery of the joint face may be crenu- late, or low ridges may extend inward for a short distance toward the central canal. In the Atele- crinida> transverse fukral ridges with deep fossae on either side occur, which resemble those at the articulations between the columnals in the larval stem, and there are sometimes traces of trans- verse ridges in other types. In its usual form this articulation is syzygial. like that between the centrodorsal and the topmost columnal. As noticed b}- W. B. Carpenter, each of the cirrals in Antedon bifida is perforated by an axial canal (part
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