Victorian Fossilf<, Fart XII. 317 



mill. Len<^th of py<2:idiuiu (Fig. lU), 9 uiiii. ; width, about 15 

 111111. ; length of axial lobe, 8 niiii. ; a,iiterior width of ditto, 

 3.75 mm. ; width of margin, about 1 mm. 



Observations. — The material in the present series of lime^ 

 stone specimens shows only the cephala and pygidia preserved, 

 the thoracic portions being disarticulated and so damaged as 

 to make it difficult to decipher more than a few isolated 

 pleurae. TTiere is very little doubt about the pygidia here 

 regarded as belonging to the cephala of Ftychnparia, as they 

 show similar superficial tuberculations, and by their numerous 

 segments they show further relationship to tliat genus. Nofc- 

 witlistanding the variability ot" form in species of this and other re- 

 lated trilobite genera, it seems advisable to regard the specimens 

 represented by Figs. 1, 4 and 6 as parts of a distinct form, next 

 described. 



Affinities. — The larg-e cephalon, witli its conico-cylindrical 

 glabella and wrinkled boi'der, shows the relationship of the 

 above species to Ptychoparia. It is a member of the Olenidae 

 on acootmt of its large free cheeks, which cut the anterior 

 mai'gin btit do not meet, but is naturally separated from 

 Olenus on account of its tapering glabella and its large pygi- 

 dium ; and from Oleiiellus by the absence of a pygidia! spine. 

 The glabella of Ptychupariu thielei closely resembles that of 

 " OJenellus sp.'' of Mr. Etlieridge, junr. ; a species from the 

 Cambrian of South Australia. i Of that form only an imperfect 

 cranidium was found. Etheridge, in his description of this 

 fossil, mentions the genus Ptychopdria, but thinks that the evi- 

 dence indicates Olenellus rather than that genus. With the 

 additional evidence of the associated pygidia in our species the 

 comparison may be worth further consideration. 



The cranidium of Olenellus (I) f arrest i (Eth., junr., MS.), 

 from the Cambrian of Western Australia, described and figured 

 by Dr. H. Woodward,'^ resembles in some respects the above 

 species, but the glabella is more decidedly conical, and pro- 

 portionally narrower. Fig. 2a on Dr. Woodward's plate, re- 

 ferred to as a telson. resembles some fragments with genal 



1 Trans. Roy. Soc. S. Australia, vol. xxix., 1905, p. 247, pi. xxv., fig. 1. 

 ■2 H. Woodward, in Foord's " Notes on the Palaeontolosry of Western Australia." Geol. 

 Ma}f., March, 1890, p. 99, pi. iv., figs. 2, 2a, b. 



