30 H. Bolton—An Isle of Man Trilobite. 
trilobite cast, notwithstanding its fragmentary condition, is of great, 
importance, as giving a possible clue to the stratigraphical position 
of the slates in which it occurred, and also as demonstrating the 
existence of organic remains in what was formerly regarded as an 
unfossiliferous series. 
The specimen was found at Ballastowel, a hill crest overlooking 
Ramsey on the south-west, and lying midway between the familiar 
Albert Tower and Elfin Glen. 
The Skiddaw Slates are here found dipping at an angle of about 
45° to the north-west, and are a little contorted. They consist of an 
alternation of schistose slates, dark and but slightly altered slates 
and dark slates charged with well rounded quartzite pebbles. 
Quartz veins pass in all directions through the series. 
The trilobite cast was picked up from the scree immediately under 
the schistose slate and was evidently derived from that rock. 
The following diagnosis of the trilobite has been obtained by the 
examination of a wax impression. 
IMPRESSION OF Bopy AND PyGrpIuM. 
Thorax of six rings; axis convex and of uniform width; body 
rings narrow and well marked off from one another. Pleura very 
broad, twice the width of the axis; grooves deep, broadening towards 
the extremities, and disappearing a short distance from the axis; 
extremities directed backwards. Pygidium a little more than half 
the length of the thorax; width double the length ; axis flattened, 
convex, and ending bluntly in the middle of the pygidium. 
Observations.—From the presence of six thoracic rings, grooved 
pleure, and semi-circular smooth pygidium with feeble axis; the 
writer was inelined to class the specimen as an Adglina, but Dr. 
Henry Woodward has kindly pointed out that it differs from Aiglina 
in the sides of the axis being parallel along their whole length, and 
in being convex, whereas in the former the axis diminishes in breadth 
from before backwards, and is flattened. 
From a careful comparison of the specimen with others from the 
Cambrian of North Wales, Dr. Woodward is of opinion that it might 
with equal propriety be placed in the genus Asaphus as Aiglina. 
Unfortunately the specimen is too distorted and fragmentary to settle 
the point. It is very probable that the specimen belongs to one of 
the two genera, and since both are markedly Ordovician or Lower 
Silurian forms, we may take it as evidence that the Skiddaw Slates 
in the vicinity of Ramsey, are of Arenig or Llandeilo age. This 
supposition is strengthened by the occurrence of two specimens of 
Palgochorda (an Arenig form) in the same beds. 
The relation of the slates near Ramsey to the general series are 
difficult to determine until the mapping of the Island, now in hand 
by Prof. Dawkins, and the Geological Survey of Great Britain, is 
completed. 
A traverse, however, made from Porth Mooar, the commencement 
of Messrs. Harkness and Nicholson’s anticlinal,’ to Ballastowel, a 
1 Harkness and Nicholson, Quart. Journ. Geol. Soc. vol. xxii. 1866. 
