480


Journal of Paleontology 91(3):477–492


Figure 2. Petalocrinus inferior:(1–2)Mu and Lin, 1987, NIGP 73928, NIGP 73929; a, oral side of arm plate; b, aboral side of arm plate; c, lateral view of arm plate; d, front view of distal furrows; e, facet view of arm plate; (3) NIGP 163722, complete specimen showing the aboral view of a crown. Scale bar = 1cm.


flattened with the five arms articulated as during life, and only the aboral side of the crown is exposed. The aboral cup is bowl shaped, but the proximal part of the infrabasals and basals are weathered away to reveal only a subpentagonal outline. The B, C, D, and E radials are partly weathered, subequal, and subtriangular in shape. The aboral portion of the A arm is weathered to expose the ambulacral grooves. The sutures of the small cup are fairly distinct; diameter of calyx is 9mm. One first primibrachial is present and rests on the E radial


facet with its proximal and distal margins parallel. The proximal width of the first primibrachial is 3mmand the height is 0.5mm, with the same thickness on both proximal and distal margins. The first primibrachials are not clearly preserved in the other four rays, but the small gap between the facet and the arm fan suggests the existence of first primibrachials that are weathered away or covered.


The angle of the subtriangular fused arm is defined as the


angle between lines drawn parallel to the general direction of the diverging sides, exclusive of the incurved distal region (Bather, 1898). The arm angles are B, 90°; C, 105°; D, 87°, and E, 95°, with an average in these four arms of 94°. Fine-grained sculpturing is poorly preserved on the aboral side of the four better-preserved arms. The Aarm is deeply weathered to expose the weathered ambulacral grooves and ridges separating adjacent ambulacral grooves. Sixteen ambulacral grooves are on the distal margin of the A arm. NIGP 163722 illustrates that the five arms of an individual differ in their angles.


Petalocrinus stenopetalus new species Figure 3


Holotype.—Holotype NIGP 163723.


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