258 



ON THE OCCURRENCE OF THE GENUS PAL.EGEINUS 



IN THE UPPER SILURIAN ROCKS OF 



NEW SOUTH WALES. 



By John Mitchell. 



The occurrence of echinoids in Palaeozoic rocks is extremely 

 I'are, and those recorded have chiefly come from the Carboniferous, 

 from which eight species have been described, all from Ireland 

 and North America.-''' Two species have been described from 

 Upper Silurian rocks, both of which are referred to the genus 

 Falcechimis; but the fossils from which these were determined 

 were fragmentary- and some eminent palfeontologists seem to 

 doubt whether the occurrence of echinoids in Silurian rocks has 

 been satisfactorily established.! Therefore to establish beyond 

 doubt their occurrence in the Silurian system of New South Wales 

 would be of more than local interest. For this reason I am led 

 to describe and figure a fragment of a fossil which to me appears 

 clearly to belong to the Palcechinidce. 



Class ECHINODERMATA. 



Order Perischoechinid.e, McCoy {Tesselata Pom.). 



Family PAL.ECHiNiDiE, McCoy. 



Genus Pal^chinus, Scouler. 



Pal^chinus sp. 



Our fossil consists of a fragment of the middle part of an inter- 

 ambulacral area of four rows of plates. Of the two median rows, 

 each contains four whole plates and a fragment of a fifth, and in 

 each of the outer rows there are four fragmentary plates. 



* Zittel. Handbuch der Palteontologie. 

 t H. Alleyne Nicholson, M.D., D.Sc, M.A., &c. The Ancient Life 

 History of the Earth. 1876, p. 105. 



