Dr. J. R. KiNAiiAN on the Genus Oldhamia. 



555 



fore, subject to tlie action of different currents, or else in their greatest abun- 

 dance, or decay, at different seasons) will be found to abound among the drift 

 at distinct periods. 



It is remarkable, also, that Old. antiqua, though the stations in ■which it 

 occurs are numerically nearly equal to those in which 0. radiata is found, yet 

 neither are the series of beds as well marked, nor the specimens, as before 

 stated, as numerous. 



The beds in which the fossils of both species occur are remarkable for being 

 permeated by those long, rounded fossils to which I drew attention in a paper 

 read before the Geological Society of this city in November, 1856 ;* and sub- 

 sequently described more in full before the same So- 

 ciety, and also in a communication laid before Sec- 

 tion C, British Association, September, 1857 ;t and 

 then proved to have been the tracks of wandering 

 worms, and also of worms of a type probably allied to 

 the covamon Arenicola inscatorius. The openings of the 

 burrows of three of this latter type are figured in Fig. 6. 

 These annelidan tracks generally are most abundant in 

 the beds above the layers of Oldhamia, and sometimes 

 passing from the beds beneath these to the bed above 

 They afford a strong proof of the former organic nature 

 of these fossils, as the worms which formed them pro- 

 bably derived a great portion of their nourishment from 

 these decomposing zoophytes. 



Fig. 6. Convolute polypidom, 

 Oldhamia antiqua. — The fasci- 

 culi of branchlets developed on 

 one side of axis only; three 

 pair of openings of burrows of 

 Arenicolites didyma (^Salter ?) 

 are shown. Bray Head, beyond 

 Brandy Hole. 



DESCRIPTION OF GENUS AND SPECIES. 



Oldhamia {Forbes). 



Polypidom rooted, plant-hke, variously branched, stemmed, or the branch- 

 lets arising from a central point ; stems erect or creeping ; branchlets irregu- 

 lar, dichotomous ( ?) ; cells biserial, alternate or subalternate. 



* Journal of the Geological Society of Dublin, vol. vii., p. 184, Plate v.. Figs. 1, 2, 3, 4, 5: 

 — " On Annelidoid Tracks in the Rocks of Bray Head." 



■j- Journal of the Geological Society of Dublin, vol. viii., p. 68, Plate vii., Figs. 1,2: — " On the 

 Zoological Relations of Bray Head and Howth, with an Account of the FossUs of Irish Cambria." 



