1896. ] OF THE PALHOZOIC OPHIUROIDEA. 1037 
Ophioteresis (Bell, 1. pp. 178-9, pl. xi. figs. 1-5), there are no 
ventral arm-plates, but this is very exceptional among recent 
members of the group. 
Family 1. OPHIURINIDS. 
Diagnosis.—Streptophiure with ambulacral ossicles, only slightly 
united, and without ventral arm-plates. 
Genus 1. Oputurra, Stiirtz, 1890 [16. p. 232]. 
Diagnosis—Dise circular, with marginal plates. Ambulacral 
ossicles long, narrow bars. Syngnaths rod-shaped. Adambu- 
lacral plates absent or altogether lost from the fossil. 
Distribution Lower Devonian, Bundenbach. 
Type species.—Ophiurina lymani, Stiirtz, 1890. 
Genus 2. Tremataster, Worth. & Mill. 1883. 
Diagnosis.—Dise with concave interbrachial outlines. No mar- 
ginal plates. Ambulacral ossicles short. Adambulacrals present. 
Distribution.—Chester Limestone, Lower Carboniferous, Llinois. 
Type species.—Tremataster difficilis,; Worth. & Mill. 1883 [19. 
p. 330, pl. xxxi. fig. 3]?. 
Family 2. LAPWORTHURIDG. 
Diagnosis.—Streptophiuroida without ventral arm-plates or 
buccal shields; ambulacral ossicles fused, but their articulating 
surfaces are plain. Madreporite dorsal. 
Genus 1. LapworTHURA, nov. gen. 
Diagnosis.—Dise circular, well-marked. Arms very flexible, 
broad ; at first uniform in width and then tapering slowly. Ambu- 
lacral 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 miltoni (Salter), 1857 (13. p. 330, 
pl. ix. fig. 4; 14]. 
The arm-structure is shown in fig. 5. 
Fig. 5. 
Lapworthura: diagram of the arm-structure, seen from ventral side. 
1 The Protaster decheni. Dew. (Ann. Soc. géol. Belg. vol. viii. 1880, pp. 52-54, 
pl. iii. figs. 1-2), is probably also a member of this genus. 
