450 CARBONIFEROUS TRILOBITES OF AUSTRALIA, 



6)6s. — Aswill be apparent from a comparison of the above 

 description with that of P. derbieitsis Martin, the two fossils 

 agi-ee in several important features. For example, in both the 

 glabella is parallel-sided and practically smooth, anterior facial 

 sutures rather straight and close to the axial furrows, eyes reni- 

 form, pygidial axis with thirteen rings, and ten segments in the 

 pleur?e; and the pygidial borders obsolescing before reaching the 

 articulating face; in the equality of maximum widths of the axes 

 and pleurae of the pygidia (this is only true in the case of the 

 above species when the pleurae are measured obliquely, and not 

 the actual horizontal widths: if measured in the latter way, the 

 axis is wider than one pleura) and the faint tendency to orna- 

 mentation on these parts. Against these resemblances, there 

 are the following differences to be considered. The length of 

 the glabella of the local species, measured from the neck-furro\v 

 to its front, is equal to its width between the axial furrows 

 across the basal lobes; in that of J\ derbiensis, these dimensions 

 are respectively about 4 : 2. The eye-lobes are shorter, and the 

 frontal border wider, neck-ring more intensely arched posteriorly 

 in the local form than in the British one. The distinct lobation 

 of the bases of the neck-ring, relatively short cephalon, and the 

 almost equality of the lengths of the cephalon and tail are very 

 marked features in the local species, separating it from the other. 

 Then tliere is the distinct, though fine, granulation, more or less 

 tuberculation of the pygidium of the form now described, as 

 against a practically smooth one in the other. Further, judging 

 from the anterior pair of pleural segments of the pygidium, the 

 thoracic pleural ribs were not imbricated, in the case of the local 

 species. Although undoubtedly closely related to each other, I 

 have concluded that the differences between them are sufficient 

 to justify their separation specifically. 



The glabellie of the above species and Proetus inissourieiisis 

 are much alike. I am indebted to J^rigadier General Vogdes' 

 paper [op. cit., antea) for the references made to American Car- 

 boniferous trilobites. 



Lvc. and Uor. — Neighbourhood of Port Stephens, probably 

 from near Bulladelah. Carboniferous. 



