Victorian Fossils, Part VIII. 25 



Gregopiura sppyi, gen. et sp. nov. 

 (PI. VI., Fig. 1 ; PL VIII., Figs. 1, 3). 



Description. — This species is quite the largest ophiurid known 

 from Australian rocks, since it must have covered a circular area 

 having a diameter of at least 72 mm. The oral framework is 

 well-preserved as a limonitic cast, the live rhomboidal groups 

 being distinctly separate. The angle made by the junction of 

 the elements con)posing the mouth-frame and the jaws is strongly 

 marked. The jaw plates are laterally slightly concavo-convex. 

 The mouth-frames near the junction of the arms are partly 

 supported by the embracing character of the ambulacrals. The 

 ossicles of the arm consist of subtriangular ambulacrals having a 

 sinus on the distal face for the passage of the podia, whilst the 

 proximal face is broadly excavated ; extending from the proximal 

 end of each ambulacral is a slender ambulacral, and apparently 

 fused to this, and at right angles, is a spine-bearing plate, having 

 generally two strong spines, one directed outwards, the other 

 towards the arm tip. 



Dimensions. — 



Length of longest arm - - - - 32 mm. 

 Width of arm at base - - - - 3 mm. 



Length of ambulacral ossicles - - circa 1 mm. 



Length of syngnaths - - - - L75 mm. 



Observations. — The above type specimen is named in recogni- 

 tion of its finder, Mr. F. P. Spry, who has kindly presented it to 

 the National Museum. This specimen is very nearly perfect, as 

 it shows the whole of the oral framework and the live arms, one 

 of the latter being only slightly damaged by fracture. The 

 ophiurid lies on the slab of mudstone with the arms undulate 

 and grouped toward one side. The flexure of the arms points to 

 the particularly free character of the ossicles in regard to move- 

 ment. The deposition of sediment upon this brittle-star must 

 have been very quiet and gradual, for even the superficial con- 

 tour of the central area of the animal has been preserved, show- 

 ing it to have been strongly convex. 



Horizon and Locality. — Silurian (Melbournian). In the blue 

 and ochreous shale of the Yarra Improvement Works, S. Yarra. 



