90 
BULLETIN OF THE LABORATORIES 
Genus ACIDASPIS, Murchison. 
I. Acidaspis Ortoni, n. sp. 
{Plate VIII, Fig. 1.) 
Acidaspis , D. U, Bull., Vol. I, p. loi, pi. XIII, fig. 23. 
Head semi-circular in outline, moderately convex in the regions 
of the glabella, suddenly depressed along the movable cheeks, the gen- 
eral effect being to give the head a very convex appearance. 
Glabella complex in structure, three-fourths as long as broad; 
mesial lobe oblong, its length equal to twice the breadth, with three 
lateral pairs of lobes ; the first pair very small, and near the obtuse 
anterior border; the second pair of moderate size ; the last pair large, 
oblong, occupying almost half the length of the mesial lobe ; the two 
posterior pairs of lobes distinctly separated from themselves and the 
fixed cheeks by furrows, from the mesial lobe by deep grooves. Fixed 
cheeks provided with a furrow extending from the posterior part of the 
eyes to the anterior part of the glabella, cutting from the fixed cheek 
a lanceolate strip, the pointed end of which lies against the anterior 
border of the middle pair of lobes; along this furrow, beginning at 
the eye, extends a narrow ridge almost to the anterior pair of lobes. 
The facial sutures anterior to the eyes begin the ridges just described, 
and then gradually separate from the same, cutting the anterior margin 
of the head with about the same curvature that the corresponding part 
of the ridge possesses ; posterior to the eyes they extend in a curve later- 
ally, then posteriorly to the posterior border of the head at a point 
slightly removed from the postero-lateral spine. Occipital ring sepa- 
rated from the glabella by a groove, of large size, laterally becoming 
depressed and attenuated, terminating at the groove which separates 
the posterior pair of lobes from the fixed cheeks. 
Movable cheeks with a raised border along the lateral edge from 
which a number of spines (about ten) extend j at the postero-lateral 
edge is quite a long spine ; from this spine a border extends along 
the posterior margin of the head, gradually becoming attenuated until 
it almost reaches the end of the occipital ring. Owing to the sudden 
and very great depression of the posterior lobes and fixed cheeks along 
the posterior border of the head, and the position of the occipital 
