BY R. ETHERIDGE^ JUXR.^ AXD JOHN MITCHELL. 659 



ments moderately geniculate. Pygidium wider than long and 

 only moderately tumid. Axis terminating submucronately, annu- 

 lations twenty-six, and cease at two-elevenths short of the whole 

 length, the first two or three usually continuous (vide Ohs.); free 

 central area bears five small tubercles, rarely more. Pleurae of 

 ten segments (doubtfully in some cases there appear to be eleven); 

 more acutely geniculate than those of the thorax, the first pair 

 with strong facets; last pair almost parallel with the axis. 



Ohs. — Foerste assigned twelve thoracic segments to E. mitchelli; 

 such, however, is not the case. There are constantly eleven, in 

 accordance with the generic definition. 



From Ecrinu7'us punctatus, Emmrich, the generic type, this, 

 the Australian type, differs by (1) — blunt instead of spined genal 

 angles; (2) — absence of spines on the fourth and tenth thoracic 

 axial segments; (3) — faceted instead of smooth lentiferous eyes; 

 (4)— absence of a true or extended pygidial mucro or telson; 

 (5) — a much less inflated and straighter-sided glabella; (6)— a 

 larger number of segments in the pygidial pleurae; and (7) — 

 smaller tubercles on the central area of the pygidial axis. Other 

 than these differences, there is a rather close affinity between the 

 Australian and European species. 



If De Koninck's description of the Duntroon specimen referred 

 by him to E. punctatus is that of the actual fossil, it must have 

 been not merely "presque complet" as he terms it, but a remark- 

 ably well preserved trilobite for a New South Wales fossil. Were 

 it not for certain points in the description of the Duntroon speci- 

 men, we would have felt inclined to regard it as E. mitchelli^ but 

 the presence of genal spines and a full pygidial mucro, or telson, 

 in the former is fatal. It is strange no Encrinurid from the 

 Silurian rocks of this State has come under our notice, possessing 

 the above features. 



An important point in nomenclature, to say nothing of the 

 morphological aspect, is the relation between E. mitchelli and 

 Cromus murchisoni De Koninck. We have already expressed 

 our disbelief in the occurrence of Cromus in New South Wales, 

 so far as published evidence enables us to judge, and our belief 



