854 TRILOBITES PROM N.S.W. 



widest across the articulating face. Greatest width 15 mm., 

 length 6 mm. approximately. Axis prominent, steep sided, 

 dorsally depressed, made up of ten rings which bore transverse 

 rows of granules, ridges narrow, prominent and traversed by 

 tine sutures, sulci deep and relatively wide; its anterior width is 

 much less than that of one side lobe, and ends abruptly at the 

 inner edge of the border with a width approximately two thirds 

 of the anterior width. Axial grooves wide and shallow. Pleura 

 mildly convex between the axial grooves and border, divided into 

 live segments, of which the fifth is faint; the first two anterior 

 pairs are at right angles with the axial line the others only 

 gently directed backwards. Border relatively wide, faintly 

 separated from the pleural segments, of which only the anterior 

 pair crosses it to the outer margin; under surface striated, the 

 ttriae being concentric and apparently seven in number. 



Obs. — I have very little doubt that in determining this 

 pygidium to belong to a species of the genus Trinucleus, the 

 determination is correct, and if so, it is the first and only part 

 of a trilobite of that genus described and figured from this State. 



The late Rev. W. B. Clarke recorded the occurrence of 

 specimens of this genus at Yarralumla and that one species had 

 been dedicated to him by Sir W. Macleay, but of those speci- 

 mens no further record was ever made, and what became of 

 them is unknown. The discovery of the pygidium above de- 

 scribed will tend to confirm Clarke's announcement with refer- 

 ence to the presence of Trinucleus in the rocks of this State. 

 (Clarke, Quart. Journ. Geol. Soc, iv., 1848, pp. 64, 66.) Yarra- 

 lumla, where Clarke said he found a Trinucleus which he could 

 not separate from T. caractici, is only two miles from where the 

 present pygidium was found. 



The Duntroon specimen resembles the pygidium of T. albidus 

 Reed (Reed, Pal. Tril. Girvan, supp. Pal. Soc, 1913, pp. 3, 4, 

 PI. 1, fig. 2) in outline, in number of axial rings in the axis 

 and in its border, but possesses fewer pleural segments, and is 

 more than double the size of T. albidus. 



No Trinucleus pygidium known to me closely agrees with the 

 one described above. In selecting a specific name I have chosen 

 to confirm the dedication of the late Sir W. Macleay. 



Loc. and horizon. — Near Duntroon homestead, Parish of Can- 

 berra. County Murray, associated with Encrinurm duntroon- 

 ensis E. and M. Evidentlv Ordovician. 



