1896.] OF THE PALAEOZOIC OPHITTEOIDHA. 1037 



Ophioteresi^ (Bell, 1. pp. 178-9, pi. xi. figs. 1-5), there are no 

 ventral arm-plates, but this is very exceptional among recent 

 members of the group. 



Family 1. OpniuniNiDiB. 

 Dlarjnosis. — 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 long, narrow bars. Syngnatba rod-shaped. Adambu- 

 lacral plates absent or altogether lost from the fossil. 



Distribution. — Lower Devonian, Bundenbach. 



Ti/]}e species. — Ophiurina lymani, Stiirtz, 1890. 



Genus 2. Trematastbk, Worth. & Mill. 1883. 



Diarjmsis. — Disc with concave interbrachial outlines. No mar- 

 ginal plates. Ambulacral ossicles short. Adambulacrals present.. 



Distribution. — Chester Limestone, Lower Carboniferous, Illinois. 



Ti/pe species. — Tremataster diffidlis, Worth. & Mill. 1883 [19. 

 p. 330, pi xxxi. fig. 3] '. 



Family 2. Lapworthu bid^. 



Diagnosis. — Streptophiuroida without ventral arm-plates or 

 buccal shields; ambulacral ossicles fused, but their articulating 

 surfaces are plain. Madreporite dorsal. 



Genus 1. Lapwoethuba, nov. gen. 



Diagnosis. — Disc circidar, 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, 

 pi. 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 Frotaster decheni. Dew. (Ann. Soc. g^ol. Belg. toI. viii. 1880, pp. 52-54, 

 pi. iii. figs. 1-2), is probably also a member of this genus. 



