112 BRITISH PALAEOZOIC ASTEROZOA. 



Australian Forms of Uranasteridse. 



Petraster smi/thi has been described by McCoy (95, p. 41, pi. x, figs, la, lb). 

 Schuchert remarks (85, p. 148) : " So far as one can judge of the description and 

 illustration, the species is a small but genuine Petraster.'' It is probable that 

 Schuchert is right, but before the affinities of the form can definitely be decided, it 

 will be necessary to undertake its further study. The species is stated to be very 

 rare in the fine sandy Upper Silurian rocks of Moonee Ponds, Flemington, a little 

 north of Melbourne. 



Section B. — Family Lepidactinid^;, nova. 



1899. Lepidasteridse (pars), Gregory, G-eol. Mag., dec. iv, vol. vi, p. 352 (see also p. 47 of this 



Monograph). 



1900. ,, (pars), Gregory, Lankester's Treat. Zool., vol. 3, Echinoderma, p. 255. 



1914. ,, (pars), Gregory (emend. Schuchert), Fossilium Catalogus, Animalia, pt. 3, p. 7. 



1915. „ (pars), Gregory (emend. Schuchert), Bull. 88, U.S. Nat. Mus., p. 157. 



Asterozoa with broad adambulacralia occupying almost the whole of the oral 

 surface throughout the greater part of the arm. Surface of adambulacralia in 

 the distal two-thirds of the arm evenly rounded and ornamented with stout short 

 spines. Proximal adambulacralia modified. Infero-marginalia and radialia recog- 

 nisable. Mouth-angle plates very prominent. Madreporite very large and oral 

 in position. 



All the English forms are from one locality and horizon, the Wenlock (Middle 

 Silurian) Limestone of Dudley. One does not seem to have any really good clue 

 to their ancestry, but they appear in many respects to be more closely related to 

 the Asteroidea of Section A than to any of the other Asterozoan branches. The 

 most primitive genus, Lepidactis, has much the same structure as early " Meso- 

 ptdceasters," except that (1) the adambulacralia are broader and more convex, and 

 (2) the very large madreporite is oral in position. The Family contains two 

 genera : 



Lepidactis, nov. gen., primitive five-rayed forms having distinctly differentiated 

 radialia, supero- and infero-marginalia. There is one species, L. wenlochi, n. sp. 



Lepidaster, Forbes, modified multi-armed forms. Extra apical plates are 

 added, and the radialia and marginalia lose much of their differentiation. There 

 is one species, L. grayi, Forbes. 



Lepidaster has one very distinctive feature. The proximal insertions of the 

 inter-adambulacral muscles were placed in round small deep holes near the oral 

 surface and are very distinctive if the ossicles have been slightly displaced 

 (PI. VII, fig. 2). Unfortunately the conditions of preservation of Lepidactis do 

 not allow me to be sure of the same type of muscle-insertion there. If it were it 

 would make a really good Family-character. 



