FEB 26 1892 



199 



ON THE OCCURRENCE OF THE GENUS PAL.EASTER 

 IN THE UPPER SILURIAN ROCKS OF VICTORIA. 



By R. Etheridge, Junr. 



(Plate XXX.) 



The Upper Silurian rocks of Victoria have so far yielded two 

 species of Asteroidea, and one well defined species of Ophiuroidea, 

 whilst a second doubtful species of the latter class is believed to 

 exist. The former are Petraster Smythii, McCoy,*" from the 

 Moonee Ponds beds, and UrastereUa Selwi/nii, McCoy, f from near 

 Kilmore. The single described species of the second class is 

 Protaster brisingoides, Gregory,! from Moonee Ponds, the doubt- 

 ful one being a MS. name Tceniaster aiostralis, McCoy. It has 

 been suggested that this is merely a synonym of Gregory's P. 

 brisingoides. 



In the genus Palccaster, Hall, the structure of the arms on the 

 actinial side consists of two rows of ambulacral plates, and two 

 rows of adambulacral plates, bordered on each side by a row of 

 marginal plates. In UrastereUa, McCoy, adambulacral plates are 

 present as in Pakeaster, but marginal plates do not exist. In 

 Petraster, Billings, on the other hand l^otli adambulacral and 

 marginal plates are developed, but separated by a row of disc 

 plates ; while in Pal aster ina, the disc itself is much extended, and 

 the adambulacral plates in the interradial angles are large and 

 triangular. 



I now purpose describing a star-fish in the Museum Collection, 

 from Moonee Ponds, which certainly appears to have the structure 

 of Pakeaster, Hall, rather than that of either of the genera named. 



Pal^aster meridionalis, s]). nov. 



(PI. XXX., fig. 16 & 17.) 



^S*;). Char. — Body small; rays moderately long and rather acutely 

 pointed, fifteen millimeters from the actinial centre to the apices; 

 interbrachial angles broad and obtuse; abactinial surface unknown. 

 Ambulacral avenues wide in comparison to the size of the body, 

 deep, very gradually tapering, the sides more or less straight 

 walled ; ambulacral plates about twenty in number on each side, 

 transversely oblong, bearing more or less pyriform pores ; adamb- 

 ulacral plates quadrangular, smaller than the marginal plates, 

 placed along the prominent edges of the ambulacral avenues ; 



* Prod. Pal. Vict., Dec. I., 1874, p. 41, t. 10, f. 1. 

 t Ihid, p. 42, t. 10, f. 2 and 3. 

 X Geol. Mag., 1889, vi. (3), p. 24. 



Dec, 1891. 



