282 BULLETIN OF THE NATURAL HISTORY SOCIETY. 
Hat and very wide, falcate genal spine. It agrees nearly with a spine 
and free cheek figured by Linnarsson, but not referred to any species.* 
The cheek portion of S. Fletcheri is very small compared with the 
spine, which is stiffened by the two sharp ridges that run along the 
middle : these ridges occupy about a third of the width of the spine, 
the rest being flat. 
The flatness and great width of the spine is one of the most obvious 
points in which this species differs from mut. Canadensis and from the 
type of & alatus. 
The pygidium of this species differs from that of the type of 
alatus as figured by Linnarsson in the possession of narrow side 
lobes (about as wide as the marginal fold) ; that author’s figure gives 
no side lobes, the marginal fold being in contact with the rachis.f 
For numbers this is the dominant species in the trilobite bed at 
Me Ad am shore, as will be seen by the following proportion of forms 
found on five square inches of surface of one of the layers. 
Sphicrophthalmus Fletcheri, 30 hds. 24 chks. 
Agnostus trisectus, chiefly the mut. ponepunctus, 9 “ 1 pi. 6 p} T g. 
Ctenopyge pecten, 8 “ 3 chks. 
Peltura scarabeoides, 1 “ 4 pi. 1 pyg. 
Parabolina Dawsoni, 1 “ 
All the heads of Sphserophthalmus were not counted ; several were 
so small that the generic characters were not well shown. 
Tarabolina Dawsoni, n. sp. PI. V, figs. §a-f. 
The middle piece of the head shield is sub-trapezoidal in form, is 
strongly arched in front, where there is a narrow but prominent 
marginal fold, and has triangular projecting posterior angles. The 
glabella is cylindro-conical in outline, and is as broad as its length 
and half of the width of the occipital ring ; it is as broad opposite the 
first furrow as at the occipital ring, and thence narrow more rapidly 
to the front, which is strongly arched ; the front margin is correspond- 
ingly arched, and the intervening area of the fixed cheek is therefore 
of nearly even breadth around the front of the glabella ; the width of 
this area on the median line is two-ninths of the length of the gla- 
bella. The glabella is marked by three pairs of furrows, nearly equi- 
* Swedish Geol. Surv., Ser. C., No. 43, p. 26. PI. 2, fig. 14. 
-tSverig. Geolog , Undersokning, ser. c, No. 43, p. 7, tafl. 1, fig. 10. 
