Art. XV. — TJie largest Australian Trilobitc hitJierto 

 discovered. 



(With Plate XI.) 



B}' R. Etheridge, Jam-., Corr. Member. 



[Read 14th December, 1893.] 



Amongst a large suite of interesting fossil organic remains 

 discovered by Mr. George Sweet, F.G.S., at Delatite, is what I 

 take to be a large ill-preserved Trilobite pygidium, at any rate I 

 can see no other feasible explanation of the specimen. It consists 

 of a Crustacean plate on the surface of a piece of flaggy calcareous 

 shale, compressed flat, and somewhat obliquely distorted. In its 

 original condition, it must have been sub-semicircular, and rather 

 acuminate posteriorly, six inches across the anterior, or pygidio- 

 thoracic edge, and with the lateral angles rounded. The longitu- 

 dinal (oblique) measurement is four and a half inches, but in the 

 undistorted state this would probably represent about five inches. 

 On the left hand side, when facing the observer, are five coalesced 

 pleural segments, probably portion of a sixth, and possibly a 

 seventh, the two last very faintly preserved. On the right hand 

 side four only are visible, as the remainder are hidden by an 

 intractable coating of matrix, which also obscures any trace of 

 axial segmentation. If, therefore, my conception of this fossil 

 be correct, it exhibits, as it should do, and allowing for the 

 oblique distortion it has undergone, bilateral symmetry. It is 

 unfortunate that the central portion is so completely hidden by 

 matrix that cannot be removed, for on the axial features, the 

 question of generic identity depends. The entire surface is 

 minutely pitted ; and the point that appears to represent the 

 apical centre, or centre of the posterior margin, is apparently 

 emarginate.* 



The principal points which militate against the Trilobite 

 nature of our fossil are: (1) the absence of any trace of axial 



'^ Too much stress, however, cannot be laid upou this point, owing to the condition of the 

 specimen. 



