OF NBW SOUTH WALES. 2X7 



or such as specially characterise, by their number and variety, 

 the strata in which they are found here. 



I am naturally much assisted by Prof. Koninck's work, in 

 which several of the Silurian species found in the Yass and 

 Hume beds are described. 



Cheirurus insignis. Fig. 8, PI. 6. 

 This specimen so exactly coincides with the description of the 

 pygydium of Prof Koninck* in having four pairs of ribs, the last 

 pair of which form a rudimentary spire following the direction 

 of the axis, that there can be no doubt about its identity. All 

 the species I have yet obtained agree in the above particulars ; 

 but the relative lengths of the lateral portions do not seem 

 to be constant. The specimens of this part of the Cheirurus 

 insignis are associated, chiefly in the lower portion of the Hume 

 beds, with other portions of Cheirurus (Figs. 5, 6, 7 ; PI. 6); but 

 1 have not been able to obtain a specimen in which the different 

 parts are united, 



Bronteus. 



As there is some difference in the terms used by different 

 writers in naming respectively the three principal segments of 

 Trilohites, I may observe that I shall in my descriptions call the 

 anterior portion the head segment, the middle portion the thorax, 

 and the posterior portion the pygidium. 



As the exact form of the head, and disposition of the eyes of 

 this genus, do not appear to be well-known, I am fortunate in 

 having several specimens from which these particulars can be 

 obtained. The specimen of nearly a whole Trilobite, which has 

 enabled me to give the restored Fig 5, has some of the ribs of 

 the thorax overlapping and displaced, and part of the cheeks at 

 the facial suture separated and removed. The position and size 

 of the eyes are distinctly indicated. One eye is perfect, and. 

 with a portion of the cheek, rests upon another part of the Tri- 

 lobite. A perfect impression of the external portion of the 

 cheek, belonging to a Trilohite of the same size and proportion, 

 enabled me to complete the form of this part. The form of the 



♦Reserches, 8ur les Fossiles, Paleozoiques de la Nouvelle Galle de 

 Sud, page 48. 



