BY JOHN MITCHELL. 399 



acquainted with. Because of its immense spines Mr. Etheridge, 

 Government Palaeontologist, suggested the specific name longi 

 spinis, which I have adopted. 



The stratigraphical range of the species is rather extensive, as it 

 makes its first appearance in the Phacops or Middle Trilobite Bed 

 of the Bowning series, and again in the Upper Trilobite Bed, 

 which represents a sedimentary deposit of 1000-1500 ft. in thick- 

 ness. Only two species of Phacops (like P. caudatus, and P. 

 fecundus), and another Acidaspis continue with the same per- 

 sistency, and these are its associates in both beds. In the 

 Phacops Bed it is also associated with Proetus B owning ensis,^ 

 and the other trilobites said to be associated with this species in 

 its description. In the Upper Bed it is associated with Cyphaspis 

 Bowningensis, &c. 



The largest specimens would appear to reach a length of 2|- 

 inches. The largest specimen (fig. 12) I have obtained for six 

 segments of the thorax and head gives a length of If inches, of 

 which the head measures f inch, and the 6 segments 1 inch. 

 Allowing ^ inch for the three missing segments and ^ inch for the 

 length of pygidium would give the length as above for the 

 complete specimen. 



In Proc. Linn. Soc. N.S.W. (2), II., two very imperfect heads 

 of this species are figured by M. Ratte, Geologist Aust. Mus. 



EXPLANATION OF FIGURES. 

 Plate 16, Vol. II. (2 Ser.), Part 4, 1887. 

 Fig. 7. — Head of small specimen. Nat. size. 

 Fig. 8. — Pygidium ,, ,, Nat. size. 



Fig. 9. — Free cheek with eye. Nat, size. 



Fig. 10. — Pleura with spine and appendage from below. Nat. size. 

 Fig. 11. — Young imperfect specimen, f Nat. size. 

 Fig. 12. — Fragment of large specimen slightly reduced. 



*In describing this species I inadvertantly stated that it was obtained 

 from the Lower Trilobite Bed, instead of from the Phacops Bed ; and failed 

 to notice the error when the proof of the paper was submitted for correc- 

 tion. 



