Original Description: "Oblong, distinctly trilobed; length two to three inches;
width three fourths
the length, central lobe rather more than one third the whole width. Proportional length of head,
thorax and pygidium about as 9, 8, 61/2. The head is transversely oval in outline, the width twice
the length, rather evenly convex, most prominent in the centre, the front margin broadly rounded,
the posterior margin trilobed by the dorsal furrows which are extended forward to about the middle
of the head but are only distinct for about one fourth that distance; they at first incline towards
each other and then becoming very obscure curve outwards; on each side of the central lobe the
posterior margin is nearly straight as far as the eye when it gradually curves forward and outward for
one half the lenght of the head when turning a broad rounded angle it merges into the front margin. In
consequence of this peculiar form of the posterior margin the genal angle in this species is in the front
half of the head. The eye is moderate size, lunate and within one fourth of its length from the margin.
The facial suture curves forward so as to cut the front margin considerably within a longitudinal line
drawn through the eye; behind the eye its course is remarkable as it turns outwards and runs parallel
with the margin which it reaches at about three fourths the length of the pleurae. The lower angle of
the eye is distant from the dorsal furrow a little less than half the width of the central lobe of the
posterior margin. The width of the cheek piece on a line drawn transversely across the head of
one third the distance from the eye to the front is nearly equal to half the distance between the eyes.
In a vertical view of the head neither the full width of the cheek piece nor the position of the genal
angle can be seen as the outline is for-shortened, consequently in the figure given the width appears
less than it really is." "Thorax of ten articulations, axis of thorax square, the lenght and breadth being the same,
moderate convex , well defined; the fulcra of the pleurae are at about one third of the width of the axis from
the dorsal furrow, the intervening space flat." "Anterior edge of pygidium convex at the axial lobe,
obliquely truncated from the fucrum, the axis either not at all or only very obscurely defined."
"Surface smooth with the exception of the front of the head where there are at the margin the usual
transverse furrows."
This trilobite is peculiar in that the enrolled shell is not globular but more or less cylindrical
or somewhat fusiform, except for the place where the anterior and posterior margin meet, where
there is an angularity. The central lobe on the thorax is nearly half the width, the lobes are quite
faintly indicated on the pygidium and not strongly on the cephalon. The largest specimens is 38 mm.
wide on the torax when enrolled and is about 17 mm. thick. The extended test is 55 mm. long.
(W.H TWENHOFEL. Geology and paleontology of the Mingan Islands Quebec. Geological society of America special paper number 11
june 4, 1938)
İRoger Barriault
