DESCRIPTIONS OF TWO NEW TRILOBITES, AND NOTE ON 

 GEIFFITHIDES CONVEXICAUDATUS MITCHELL. 



By John Mitchell, late Principal of the Newcastle Technical College and 

 School of Mines, Newcastle, N.S. Wales. 



(Plate liv.) 



[Read 29th November, 1922.] 



P'HILLIPSIA CONVEXICAUDATA. 



Griffithides convexicaudatm, Mitchell, Proc. Linn. Soc. N.S.W., 43, 1918, 

 475-9, PI. xlvi., flg. 13, PL xlviii., figs. 1-3, PL Hi., figs. 5, 6. 



Recently Mrs Pincombe, of Lambton, had the good fortune to find a perfect 

 specimen of a trilobite, belonging to the genus PhilKpsia, .at the same locality 

 on the Glen William Road, near Clarencetown, as Griffithides convexicci/adatus 

 Mitch., was found some years ago. This tine specimen has been passed on to 

 me for identification and description, for which I am very thankful, as it 

 enables me to revise my former description and conclusions regarding the generic 

 position of that species. In the first place, after much careful study of this 

 new specimen in conjunction with G. convexicaudatus Mitch., I find the differences 

 insufficient to justify their specific separation; and as the new fossil is a Phillip' 

 sia, the species convexicaudatus must be transferred to that genus. Between the two 

 there are small differences; — for instance, in the original type the thorax and 

 pygidium are of equal length, and the cephalon so little shorter than either of 

 these that the three parts may be accepted as almost equal; in the case of the 

 new form the lengths of these parts are: head, 3.9 mm., thorax, 4.7 mm., tail, 

 3.9 mm., but the latter is, if they are specifically identical, not more than half 

 mature, and this may account for the discrepancies in the relative dimensions. 

 Another difference appears in the eyes: those of the original type seem to be 

 shorter and deeper than those of the other; but the cephalon of the former is 

 very imperfect, and this difference may arise through distortion. The head of 

 the recently-found form shows all the characteristic features of a Phillipsia near 

 P. darhiensis, and could, it appears to me, be placed as a variety of that species. 

 In a general way every feature of the cephalon of our new trilobite agrees with 

 the similar part of the cephalon of P. darhiensis. They are similar in shape, 

 bear similar glabellar furrows, have eyes identical in shape and position and re- 

 lative size; in fact the head-shields of the two forms are practically identical, 

 and if the specific determination were made on this part of our new form alone, 

 it would certainly be placed with Phillipsia darhiensis Martin. The two Austra- 



