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Abstract

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In accordance with the suggestion of Howell and Stubblefield and subsequent workers, Helenia has been reinterpreted as a hyolithid appendage. Isolated specimens of the Early Cambrian H. bella Walcott are flattened, are bladelike in cross section, and have an elaborate, irregular ornament covering both surfaces. The specimens are strongly arched and slightly twisted in the third dimension. Presumably these were paired structures which extended outward from openings between the shell and the operculum of the hyolithid and curved down to touch the substrate midway along their length and then upward and posteriorward at the tips. As suggested earlier, their prime function was to provide lateral stability. There is no obvious way that these appendages could have played a major role in locomotion. However, the upper edges of the appendages could have acted as a fulcrum for the operculum; contraction of small muscles running between the operculum and the appendages assisted the ventral part of the operculum to swing upward.