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Show 1038 DR. J. W. GREGORY ON THE CLASSIFICATION [Dec. 15, Genus 2. PURCASTER, Stiirtz, 1886 [15, p. 79]. Diagnosis.-Disc circular small. Arms short, narrow, slightly flexible, tapering gradually. Ambulacral ossicles of a long central body and two short wings, which are attached only to the anterior corner of the ossicle. Distribution.-Lower Devonian, Bundenbach. Type species.-Fur caster palceozoicus, Stiirtz 1. Remarks.-In Stiirtz's description he refers to the existence in this genus of ventral arm-plates, and even figures them. His type specimens are now in the British Museum, but I cannot verify the existence of any ventral arm-plates. His type (B.M. E 3805), for example, seems to m e to show almost conclusively that an open furrow ran along the underside of the arm. Genus 3. PALASTROPECTEN, Stiirtz, 1886 [15. p. 88]. Biagnosls.-Disc circular, large (badly preserved in the specimens ; probably originally soft and irregular). Arms thick, broad, and somewhat lanceolate in shape. Ambulacral ossicles narrow, tbe lateral wings resting on the whole body of the ossicle. Distribution.-Lower Devonian, Bundenbach. Type species.-Palastropecten zlttell, Stiirtz, 1886 [15]. Aganaster, sp., Miller & Gurley [12. p. 57, pl. ix. figs. 10, 11], seems to m e to be allied to Lapivorthura, and at least a member of the same family. It apparently has no ventral arm-plates, but an open furrow, and thus differs widely from Aganaster It is probably a new genus. Family 3. EOLUIDID^E. Diagnosis.-Streptophiurae with the ambulacral ossicles united to form vertebral ossicles. Ventral arm-plates present, but there are no buccal shields. (Dorsal arm-plates present only in the highest genus.) Remarks.-This family includes three Devonian genera, which differ from the previous families of this order by the presence of ventral arm-plates and by having vertebral ossicles, which articulate (? always) by simple rounded pits and processes. The family differs from living Streptophiurae by the absence of buccal shields and the simplicity of the oral armature. Genus 1. EOLUIDIA, Stiirtz, 1886 [15. p. 89]. Diagnosis.-Disc rather large; the interbrachial outlines are deeply concave. Each syngnath consists of pairs of mouth-frames and jaws; a jaw-plate is present. The vertebral ossicles are small and the union of the two lateral elements incomplete ; the lateral 1 The Protaster daoulasensis, Davy (Bull. Soc. geol. France, ser. pp. 182-187), is an ally of Furcaster. |
