BY JOHN MITCHELL. 437 



the four anterior and missing segments of my specimen would 

 have a length equal to the six that are present, which would 

 make the axis twice as long as wide. Pleurte long g'^gths in. 

 (■781 mm.). Length of spine iuths in. (2-6 mm.). Pygidium 

 long ^ths in. (2-86 mm. nearly), wide J*ths in. (3"6 mm.). 

 Rudimentary axis wide |; (about) or ^ the total width of 

 pygidium. Total length of specimen t^ths in. (12.4 mm. nearly). 



The subrudimentary chaiacter of the pleurae of the thorax, their 

 long spines, and the great proportionate width of the axis are the 

 striking features of this species, and distinguish it from all I am 

 acquainted with, and certainly from either of those yet recorded 

 from Australia. The specimen here described, which is of immature 

 growth, has six segments of the thorax with pygidium attached 

 nearly perfect. The four front segments have l)een obliterated 

 by the head which has been turned backwards upon them. Some 

 heads which I have obtained have double the dimensions of this 

 specimen, and would therefore belong to individuals more than 

 1 inch long. 



The test of the thorax and pygidium of this species must have 

 been of a delicate character, for though heads are numerous, it 

 is rare to obtain even a fragment of these two parts. 



This fossil occurs in the lower Trilobite Bed of the Bowning Sei'ies, 

 associated with representatives of the genera Acidaspis, Encrimirtis, 

 Proetus, Cromus, Ilarpes, <kc. Two of the associated species have 

 been identified by F. Batte, Esq., as Acidaspis VerneuUi (?), and 

 Proetus Ascanius (?), vide Proc. Linn. Soc. of N.S.W. 1886, 

 pp. 1066-7. (1) 



Locality. — Bowning. From a specimen in ray collection. 



(1) When I submitted the fragments of A. VerneuUi, which are here 

 described by Mr. Ratte, I had not obtained a pygidium tliat beyond doubt 

 belonged to the same species as the head and fragment of thorax here referred 

 to ; but since then I have obtained several pygidia attached to fragments 

 of the thorax of this species ; and they agree in character with the descrip- 

 tion given of the pygidium of A, VerneuUi by Barrande. Hence the doubt 

 which Mr. Ratte had on account of the absence of a pygidium, must I think, 

 be set Ht rest ; and Mr. Ratte's identification of A. VerneuUi for the 

 species, be confirmed. 



