484 SILURIAN TRILOBITES OF NKW SOUTH WALES, vi., 



possessing the double curve referred to in Barrande's description 

 of C. incerta, and this seems to us to be a feature present in 

 other species of CalymetLe. The pleurae in Bar rand e's species are 

 represented as depressed towards the axis and rising towards the 

 fulcra, and then dipping at right angles; the pleurae in our form 

 slope ve7'y gently from the axial grooves towards the fulcra, and 

 then turn downwards at an angle much greater than a right 

 angle. The axis of the pygidium of C. iucerta is represented to 

 be nearly as wide as the pleura?, and reaches nearly to the edge 

 of the border. In our form, the pleural lobes of the pygidium 

 are much wider than the axis, and the axis terminates much 

 short of the edge of the margin. Centrally, under the terminal 

 piece of the pygidial axis, there is, in ours, a distinct arch. In 

 other respects, the two pygidia agree. Finally, it seems to us 

 that, in our form, we have a species possessing a cephalon in 

 which are blended the characteristic features of C. tuberculosa 

 and C. iiicerta, the thorax of C. tuberculosa, and a pygidium re- 

 sembling that of C blumeubachii and 0. iucerta. VV^e have, 

 therefore, reluctantly been unable to place it with either of 

 those species. 



It was only after the above description, etc., of G. australis 

 was completed by us, that we became aware of Mr. Chapman's 

 paper on Victorian Fossils, Part xviii., in which occurs his de- 

 scription of C. angustior. With this species^ we have now to 

 compare the Bowning form. As we have shown in the case of 

 C. australis, Mr. Chapman points out that his species resembles 

 C. tuberculosa Dalm., and C. blumenbachii Brongniart, and, 

 therefore, possesses features represented in the Bowning form. 

 It would not have surprised us to have found our species iden- 

 tical with Chapman's C. anyustior; but, judging from description 

 and illustrations of it, we must claim for ours separate specific 

 rank. Mr. Chapman depends mainly on the relative narrowness 

 of the form in his species, and particularly of the glabella, for 

 its separation from C tubercAilosa and (J iiiat/areiisis. It is 

 questionable whether a mere diflferencH of form of this kind is a 

 sufHcient basis for the erection of species. Certainly another 

 feature, the bifurcation of the distal ends of the pygidial ribs, is 



