58 CARBONIFEROUS TRILOBITES 



entire, smooth, broad ; general surface smooth, and destitute of ornamentation of 

 any kind save a simple rib-like furrow and ridge where the pygidium unites 

 with the free thoracic segments. 



Formation. — Carboniferous Limestone. 



Locality. — Moneenalion Commons, Co. Dublin. From the Survey Museum, 

 Dublin. Kindly lent by Prof. E. Hull, M.A., LL.D., F.R.S., Director. 



The specimen here described is the same recorded by Mr. W. H. Baily, F.L.S., 

 in the Explanatory Memoir to Sheets 102, 112 (p. 19), as " Phillipsia Brongniarti" 

 and was obtained from the Upper Limestones on the south side of Dublin, at 

 Moneenalion Commons, about one mile south-east of Castle Bagot (Sheet 111). 

 In the Explanation of Sheet No. Ill Mr. G. V. Du Noyer wrote (p. 21) : "The 

 general aspect of the Limestone varies between that of a palish and a dark grey 

 compact rock ; it is usually very fetid, and contains layers of chert. 



" Some beds are very fossiliferous, and the Trilobite (Griffithides) is not 

 uncommon in them ; others consist almost entirely of crinoid fragments, large 

 Productce occurring sometimes in layers." 



The specimen under consideration is embedded in dark (almost black) fetid 

 crystalline limestone, full of crinoidal fragments and of Brachiopoda. 



A careful comparison of this specimen with the pygidium described by Phillips 

 (formerly called " Ph. Brongniarti," but now placed in the genus Griffithides 

 under Phillips's original name of obsoletus) has satisfied me that they cannot 

 possibly be placed together. 



" Ph. Brongniarti " = G. obsoletus compared with Proetus levis. 



(a) Axis of pygidium nearly equal to (a) Axis less than one third the entire 



half the breadth. breadth. 



(6) Axis extremely gibbous. (b) Axis but little elevated. 



(c) Pleurae very convex. (c) Pleurae almost flat. 



(d) Axis and pleurae very distinctly (d) Axis and pleurae very nearly smooth. 



annulated. 



(e) Pygidium one fourth broader than (e) Pygidium one third broader than 



long. long. 



The fact of this abdominal shield from Co. Dublin being so unlike any one 

 belonging to Phillipsia or Griffithides led me to compare it with those of other 

 genera, and I was at once struck with its resemblance to the pygidia of Proetus. 

 Seeing that in 1861, Hall had applied this generic appellation to a Carboniferous 

 Trilobite from America, there cannot, I think, be any very great objection to 

 its use here. 



The pygidium is certainly new, and agrees with that of Proetus (e.g. P. latifrons) 

 better than with any other genus with which I am acquainted. 



