BY R. ETHERIDGE, JUNR., AND JOHN MITCHELL. 485 



another reason advanced; but this may be an accidental one. 

 In our species, the sutures separating the pleural divisions of the 

 pygidium always widen towards the thickened border; but the 

 divisions never show free ends, nor do those sutures cross the 

 margin. 



The chief difference between our species and 6'. aiiynstior is 

 the presence, in the former, of a fourth lateral glabella-fuirow; 

 but if future inspection of better preserved specimens of the Vic- 

 torian species, shows it to be possessed of four lateral glabel la- 

 furrows, our species will fail probably. The position of the eyes 

 in each species agrees. There is also fairly close agreement in 

 the dimensions of the two, as will be seen by the measurements 

 of our fossil given below. 



Dimensions. — The total length of the whole fossil, cephalon, 

 thorax, and pygidium, and the width between the genal angles 

 are respectively as follows, for three specimens, in mms. — No. 1 : 

 59, 16, 32, 10, 37. No.2 : 73, 18, 39, 16, 40. No.3 : 54, 16, 28, 

 10, 38. The averages of the three are: — 62, 16*6, 30, 12, and 

 385. The dimensions are not greatly different from those given 

 by Mr. Chapman for his species; but the proportionate length of 

 the thoraces in ours seems to be, in every instance, greater 

 relatively to the other parts than in his. The measurement of 

 the specimen No.3 shows its length to be the same as the one 

 Mr. Chapman has used to obtain his dimensions, and illustrates 

 the discrepancies in the proportionate lengths of the parts. In 

 referring to the relationship of our species to C. iucertn^ we 

 omitted to point out above the great difference there is between 

 the glab«lltB of the two species. In our species, the length of 

 the glabella is only a little less than its width between the basal 

 or posterior lobes, measured from outside to outside; in C. in- 

 certa^ the width between these same lobes is very much greater 

 than is the length of the glabella. In the glabella of some of 

 our specimens, these measurements are practically equal. 



Calymene australis may well Ije regarded as the typical and 

 most characteristic trilobite of the Bowning Series. It persists 

 from the Lower Trilobite bed to the top of the series; and it 

 may be regarded as typifying the Upper Silurian Formation in 



