398 Baily— Cambrian Rocks and Fossils. 
mixed with Oldhamia antiqua, and tracks of large and smaller 
diameter (c) proceeding in a horizontal direction on the same 
surface. 
Tubular markings of a larger size and tortuous form, usually found 
in distinct beds of a coarser and more sandy character, have been 
referred to Mollusca by Dr. Kinahan.* In the absence, however, 
of any more certain evidence of the existence of this important class 
during the Cambrian period, such as their fossil shells would present, 
we cannot, I think, do otherwise than refer them with the other tracks 
to the class Annelida. 
To the late Dr. Kinahan’s perseverance we are indebted for the 
discovery of a fossil he has described under the name of Histioderma 
Hibernicum.t Several examples of the large tubular casts of this 
fossil, which he considers to have been an Annelidan worm, were 
obtained by him from the compact greenish grits overlying the Old- 
Fic. 6.— HISTIODERMA HIBERNICUM, KINAHAN, NAT. SIZE. 
a. Opening of burrow and commencement of tube. 
6. Lower portion, or curved extremity. 
Cambrian (green grits), Bray Head, County of Wicklow. 
hamia-beds of Bray Head and Greystones. Their appearance on the 
surface of the beds is that of a slightly raised mound of about one 
inch and a half in diameter, having a depression in the centre form- 
ing the orifice. These tubular burrows pass vertically through the 
bed for a distance of about one and a half to three inches, gradually 
decreasing in size, and slightly curving ; they terminate by a rounded 
extremity which turns upwards, assuming a kind of trumpet-shape, 
the cast of its upper portion being marked by several ridges cross- 
ing each other at irregular distances, as represented in fig. 6, which 
is reduced. Dr. Kinahan describes this fossil as ‘a tentacled sea- 
* Journ. Geol. Soe. Dublin, vol. vii. p. 184, pl. 5, figs. 1-5; and Trans. Royal 
Irish Academy, vol. xxiii. p. 56. 
Y~ Journ. Geol. Soe, Dublin, vol. viii. p. 71. 
