136 



BRITISH PALAEOZOIC ASTEROZOA. 



1868. Urasterella, Hall, 20th Rep. New York State Cab., p. 289 ; rev. ed., p. 332. 

 1874. „ McCoy, Prodr. Palaeont. Victoria, i, p. 42. 



1879. „ Zittel, Handb. Pakeont., vol. i, p. 453. 



1886. „ Stiirtz, Neues Jahrb. fiir Miner., vol. ii, p. 152. 



1886. Roemeraster, Stiirtz, Palseontographica, vol. xxxii, p. 85. 



1890. Urasterella, Stiirtz, loc. cit., vol. xxxvi, p. 219. 



1890. Roemeraster, Stiirtz, loc. cit., vol. xxxvi, p. 220. 



1893. Stenaster, Stiirtz, Verb. Nat. Ver. preuss. Ebeinl., Jahrg. 50, pp. 40, 56. 



1893. Roemeraster, Stiirtz, loc. cit., pj>. 52, 73. 



1899. Urasterella, Gregory (pars), G-eol. Mag., dec. iv, vol. vi, p. 352. 

 ,1914. „ Schucbert, Fossilium Catalogus, Animaha, pt. 3, pp. 5, 7, 28, 36, 37, 39, 44. 



1915. Schucbert (pars), Bull. 88, U.S. Nat, Mus., pp. 41, 42, 45, 47, 49, 50, 69, 164, 173, 



194, 212. 



1916. Hudson, G. H., New York State Mus. Bull., Twelfth Eeport of the Director, 1915, 



pp. 117—139. 



A history of the genus is given by Schuchert (1915, pp. 175 — 177). 

 Generic Characters. — A Urasterellid with dissimilar rows of adradialia. 



Species of Urasterella. 





British Isles. 



America. 



European Con- 

 tinent. 



Middle Ordovician . 





U. pulchella 







- 



U. medusa 

 U. ulrichi 





Upper Ordovician . 



U. thraivensis 



— 



— 



Lower Silurian 



— 



U. ruthveni, mut. arisaigensis 

 (not described) 



— 



Middle Silurian 



U. gutterfordensis 





U. ruthveni, 

 var. leintwar- 

 dinensis. 



Upper Silurian 



U. ruthveni, var. leintwardinensis 

 U. ruthveni 



— 



— 



Devonian 





U. hdher i (not described) 

 U. stella (not described) - 

 U. schucherti (not described) 

 U. nov. sp. (not described) 



U. aspernfa. 



Carboniferous 





~ 



U. in on tana. 



There appear to be several lineages represented, and we cannot with our 

 present knowledge separate them. We can take the following characters as 

 showing progressive elaboration : 



(1) An increase in size 



(2) A comparative lengthening of the 



arm 



Observed generally. 



All young English and American forms 



are much more stellate than the more 



mature individuals. 



