128 RECORDS OF THE AUSTRALIAN MUSEUM. 



On the occurrence of a STARFISH in the UPPER 

 SILURIAN SERIES of DOWNING, N. S. WALES. 



By R. Etheridge, Junr., Curator. 



Starfish have not so far been recorded from the rich fossiliferous 

 deposits of Bowning, nor was I cognisant of their presence in 

 those rocks until Mr. John Mitchell presented a specimen to the 

 National Collection. 



The rarity of this form of life in the Bowning rocks must plead 

 my excuse for describing so fragmentary an example as that now 

 referred to. The specimen is interesting, not only on this account, 

 but also from the fact that it may possibly belong to one of two 

 by no means common genera of Upper Silurian age — Pahmcoma, 

 Salter [non. D'Orb), or Palaslerina, McCoy. 



As now preserved, the Starfish consists of portions of three rays 

 and traces of the interbrachial disk, with the actinial surface ex- 

 posed. The ambulacra are deep proximally, but become faint 

 distally. The ambulacral plates are not clearly distinguishable, 

 but the margins of the valleys are bordered by a row of adambu- 

 lacral plates, quadrangular and distinct, although the presence of an 

 outer row is questionable. Combs of I'igid spines are attached to 

 the arm edges, of whatever construction they may be. The mouth 

 is very large, strongly pentagonal; the oral plates large, triangular, 

 and apparently of one piece each, instead of two, as should be the 

 case in a true Palcvocoma. The arms are united by a disk broken 

 up by a series of anastomosing lines, giving rise to the appearance 

 of a polygonal-plated integument when pressed together, but in a 

 normal condition squamose, as seen through the oral cavity. From 

 the margin of the disk stream fine long spines that in all probability 

 covered the whole of the dorsal surface. 



It must be at once admitted that, without a more definite 

 knowledge of the ambulacral plates, and in the face of single in- 

 stead of double oral plates, the reference of this form to Palceocoma^ 

 Salter, is open to doubt ; but the presence of the disk with its 

 squamose plates, laden with spines, seems to place our fossil nearer 

 to that genus than to any other. The only other genera known 

 to me that it appears to approach are Edrioaster, Billings ; Scheoi- 

 aster, M. &■ W. ; and Falasterina, McCoy. As regards the first- 

 named,* the form of the arms, and nature of the disk, are 

 characters sufficient for separation ; whilst the form of the 

 adambulacral plates in the second f genus are likewise distinct. 



* Canadian Org. Eemains, Dec. iii., 1858, p. 82. 

 t Illinois Geol. Survey Report, ii., 1866, p. 277. 



