On the Palaeontology of County Dublin. 163 



Oldhamia antlqua has the appearance of a number of small 

 fan-shaped tufts, arranged in an alternating manner, upon a zigzag 

 axis. This species is also abundant and well preserved in the 

 brown and purple slates of Carrick Mountain, County of Wicklow, 

 accompanied there, as at Bray Head, by tracks and burrows of 

 animals, which frequently occur in pairs, and resemble those from 

 the Cambrian rocks of the Longmynd in Shropshire, named by 

 Mr. Salter Arenicolites didymus and A. sparsus, species which 

 are probably identical. The late Dr. Kinahan believed he had 

 detected Oldhamia aniiqua, accompanied by tracks, in brown 

 laminated slates at " Puck's Rocks," near the " Nose of Howth." 

 The specimen he collected, and presented to the Geological Survey 

 Collection, is not, however, so distinct as those from Bray or 

 Carrick Mountain. 



Oldhamia radiata. — The most frequent form resembles a num- 

 ber of detached bunches of flattened sea-weed, without any 

 connecting axis or stem, covering irregularly the thin laminae of 

 the rock, giving it a somewhat star-shaped appearance. This. 

 species is most abundant on the shore at Bray and Greystones 

 Co. Wicklow. 



Histioderma Hibemicais a fossil from the same rocks at Bray, 

 described by Dr. Kinahan* as " the cast of a tentacled cephalo- 

 branchiate sea-worm, not very dissimilar from the common lug- 

 worm (Areuicola) of our present seas." This fossil is of consi- 

 derable size ; it may be seen occurring as mounds on the surface 

 of a large calcareous bed on the shore, a little south of the Peri- 

 winkle Rocks. These mound-like protuberances are about one 

 inch and a-half in diameter, with a central depression from which 

 proceeds a tubular opening of about half-an-inch in diameter, 

 passing vertically through the rock from two to four inches, or 

 even more, sometimes in a tortuous or curved manner. These 

 fossils are entirely confined to Irish strata, excepting the double 

 markings, supposed to be the burrows of sea-worms (annelidan), 

 named by Mr. Salter Arenicolites didymus and {A. sparsus. 

 The Oldhamia and Histioderma have not been detected in the 

 Cambrian rocks of the Longmynds, or those of North Wales. 



Haugldonia pcecila, described by Dr. Kinahan, from red gritty 

 beds, Periwinkle rocks, Bray Point, as an aggregation of the 



* Jourral of the Geological Society of Dublin, vol. viii., p. 71. 



