BULLETIN OF THE NATURAL HISTORY SOCIETY. 
2 SO 
the Geological Museum in Jermyn street, London ; on none of these is 
there any trace of a tubercle at the extremity of the mid-lobe of the 
pygidium. This indicates a closer relationship between the two Cana- 
dian forms than is borne by either of them to the type, though the 
apparent difference seems to be greater ; it appears also to show that 
the American mutations arose independently from the Longifront 
phylum. The indication is similar to that given by the development 
of Anomocare stenotoides from the Olenoid phylum, i. e., a tendency to the 
independent development of similar forms at particular stages in geo- 
logical history.* 
The differences from A. trisectus-ponepunctus, are the following : 
The head shield is more strongly arched, stiffer and smoother ; the 
pygidium is not trisected on the posterior lobe of the rachis, though 
faint furrows may sometimes be traced on one side or the other. It 
differs from the European type of trisectus, in that the median lobe 
traverses the middle part of the two anterior segments, thus interrupt- 
ing the dividing furrow between these segments, and it differs also in 
its smooth, stiff shields. 
This mutation shows a considerable resemblance to A. princeps , 
Salt f But Salter is emphatic in stating that there are no marginal 
spines to his species (nevertheless two of his figures show such spines, 
perhaps these are two species included under A. princeps ). The figure 
of Salter’s species which comes nearest ours is 16 of plate 5, but in 
that the tubercle on the glabella is represented as elongated and rest- 
ing on the middle of the main lobe, while in the Cape Breton form it 
belongs entirely to the anterior segment or somite of the main lobe. 
Sph.erophthalmus Fletcheri, n. sp. PI. V, figs. 7 a-f 
General outline of the middle piece of the head shield , square, with 
a large, nearly cylindrical, glabella, which in front overhangs the 
narrow marginal fold. The glabella has a width two-thirds of that of 
the glabella and occipital ring together. A strong furrow divides off 
the posterior third of the glabella. The occipital ring is narrower 
than this lobe of the glabella, and bears a tubercle at the middle. 
The fixed cheek is much drawn in behind and then arches down- 
ward and outward to the posterior margin. The front of the cheek is 
tumid and traversed by an ocular fillet directed diagonally backward. 
* See Trans Roy. Soc. Can., vol. iv, sec. iv. pp. 140-148. 
+ Mem. Geol. Surv. G. Britain, vol. iii, p. 488, pi. 4, figs. 2 and II «, and pi. 5, figs, la and 6- 
