DISCINIDZ. 17 
from Wellfield, the depressions left by the spines of the surface are very obvious and 
rather crowded, producing a puckered irregularity of the surface, which is not to be seen 
in most of the specimens from Pen Cerrig ; the concentric lineation is also more distant 
in the former, between which the reticular punctation is so excessively minute that 
it can only be traced with a powerful lens, in favorable lights, on the best pre- 
served portions of the shell, differing, therefore, very much from the most nearly allied 
fossil, the so-called Zerebratula hamifera, Barrande. In nearly all the specimens the 
distinct and rather large circular opening at the apex of the beak is easily seen, and in 
many specimens an irregular fissure, apparently produced by crushing, extends a variable 
distance towards the front margin, either in the medial line or more or less to one side or 
the other. The few rather large concentric waves or interruptions of growth are only 
seen in some specimens. 
“This species seems to agree in everything with the little Zerebratula hamifera, 
Barrande (‘ Haidinger’s Naturwissenschaftliche Abhandlungen,’ vol. i, p. 418, t. 20, 
fig. 9); but has the reticular punctation infinitely more minute than he describes that 
of his species to be (half a millimetre long, or four in a square millimetre).” 
M. Barrande gives the geological place of his species in Bohemia as the highest 
beds, or the quartzite stage, D, of the Lower Silurian. The schists in which it occurs in 
such profusion in Britain are, Mr. Salter says, much lower. Its gregarious habits are 
curiously shown by the circumstance of a fragment of shale, from Pen Cerrig, four or five 
inches long and wide, having afforded upwards of a hundred specimens now in the 
Cambridge Collection ; and another mass, not much larger, from Wellfield, having yielded 
upwards of seventy (M‘Coy). Iam very doubtful as to the correctness of Prof. M‘Coy’s 
comparison of his little shell with the 7. Lamifera, Barrande. 
Position and Locality. \t abounds in the Llandeilo flags at Wye Ford, Builth, 
Radnorshire ; also in the same formation at Conway Castle. In Scotland it was found by 
Prof. Harkness in the Graptolite-shales, at Lambfoot, Glenkiin Burn, Kirkeniecheal, about 
nine miles east of Dumfries; also at Garpool Burn, near Moffat, where it occurs in 
a very thin bed or layer, not more than two inches thick. A small specimen was also 
found by Mr. R. Gray at Balcletchie, near Girvan, in Ayrshire. In Ireland it occurs in 
the Lower Silurian black slates of Bellewstown, county of Meath (Irish Survey Coll.). 
