32 



BRITISH PALEOZOIC ASTEROZOA. 



The Mouth- Fnvme of Lapworthnra. — SoUas and Sollas have recently given a very 

 detailed and careful account of the mouth-frame of Lapworthnra. The following 

 account is from my own investigations and is in one or two details slightly different 

 from that previously published. The component ossicles are well differentiated. 



F, n. r. iv.v.r. 



25 



' — i — r 



26 



Ar. 



Text-fig. 25 (on left). — Inner view of jaw of Ophiarachna incrassa/a (after Ludwig). Lettering as on Plate I. 

 Text-fig. 26 (on right). — Outer view of jaw of Ophiarachna incrassata (after Ludwig). Ar., articulatino- 



face with jaw of next radiu.s ; n. r., nerve ring. 



C.(2) 11. r. 



— -I-J', 



F., 



Text-fig. 27.— Inner view of jaw of Ophiarachna incrassata, cut away to show course of canals to the first 

 two tube-feet (after Ludwig). Lettering as on Plate I. 



C.(2) 



F-s F., F, 



Text fig. 28. — Inner view of movith-parts of Stenaster ohtusus. Lettering as on Plate I. 



In fact almost the only primitive feature possessed by the mouth-frame of the form 

 is the unfused condition of the mouth-angle plates and the first ambulacralia. 



Plate I, fig. shows the mouth-frame in apical view. The radial ossicles 

 bounding the mouth are large, stout and bow-shaped. According to Prof, and 

 Miss Sollas these ossicles consist of (t^, ao, a^, and an abactinal crest of a^ and 

 possibly ftg, these elements being fused end to end. 



