Proceedings of the general meetings for scientific business of the Zoological Society of London, 1896

Page 1131

1896.] OF T H E PALAEOZOIC OPHIUROIDEA. 1037 Ophioteresis (Bell, 1. pp. 178-9, pl. xi. figs. 1-5), there ventral arm-plates, but this is very exceptional among recent members of the group. Family 1. OPHIURINID^E. Diagnosis.-Streptophiurae with ambulacral ossicles, only slightly united, and without ventral arm-plates. Genus 1. OPHIURINA, Stiirtz, 1890 [16. p. 232]. Diagnosis.-Disc circular, with marginal plates. Ambulacral ossicles loug, narrow bars. Syngnaths rod-shaped. Adambu­lacral plates absent or altogether lost from the fossil. Distribution.-Lower Devonian, Bundenbach. Type species.-Ophiurlna Igmanl, Stiirtz, 1890. Genus 2. TREMATASTER, Worth. & Mill. 1883. Diagnosis.-Disc with concave interbrachial outlines. No mar­ginal plates. Ambulacral ossicles short. Adambulacrals present. Distribution.-Chester Limestone, Lower Carboniferous, Illinois. Type species.-Tremataster dlfficills, Worth. & Mill. 1883 p. 330, pl. xxxi. fig. 3] \ Family 2. LAPWORTHURIDJE. Diagnosis.-Streptophiuroida without ventral arm-plates buccal shields; ambulacral ossicles fused, but their articulating surfaces are plain. Madreporite dorsal. Genus 1. LAPWORTHURA, nov. gen. Diagnosis.-Disc circular, well-marked. Arms very flexible, broad; at first uniform in width and then tapering slowly. Ambu­lacral ossicles with the distal and proximal margins parallel; with lateral wings curving round the podial pores. Madreporite large. Distribution.-Ludlow Series, Silurian, Ludlow. Type species.-Lapworthura miltonl (Salter), 1857 [13. p. 330, pl. ix. fig. 4 ; 14]. The arm-structure is shown in fig. 5. Pig. 5. Lapworthura: diagram of the arm-structure, seen from ventral side. 1 The Protaster decheni. Dew. (Ann. Soc. geol. Belg. vol. viii. 1880, pp. 52-54, pl. iii. figs. 1-2), is probably also a member of this genus.