486 Canadian Record of Science. 
regarded by him as a link between the first four of these 
genera and the two last, and thus most suitable for the 
family type. Within the genus there are species which 
ally it to Olenus and Peltura (L. stenotus, &c.), and also one 
(L. raphidophorus) which by its peculiar cheek-spines shows 
a relationship to Spherophthalmus and Ctenopyge. 
The most obvious distinction between Leptoplastus and 
Olenus is the position of the eyes, which in the latter genus 
are in advance of their normal position in trilobites; this 
difference is expressed by Angelin as “oculi subapicales” 
in Olenus, “oculi centrales”” in Leptoplastus. In the latter 
genus the head is more strongly vaulted transversely, and 
the genal spines spread outward in a more decided manner 
than in Olenus. There are other differences, as the number 
of segments in the thorax, form of the pygidium, &c., which 
are not so easy to determine. 
By the form of the head, &c., the Acadian species belong 
to Leptoplastus, and though we have not sufficiently perfect 
specimens to reproduce all the characters as given by 
Angelin, those known are sufficient for a description of the 
species. 
LEPTOPLASTUS STENOTOIDES. N. Sp. 
Head. Broadly semi-circular; crust, smooth. Centre 
piece of the head-shield sub-trapezoidal; strongly arched 
transversely, depressed in front of the glabella; marginal] 
fold distinct, elevated. Glabella ovate-cylindrical, indented 
on each side by a pair of furrows which are moderately 
inclined backward. Occipital furrow distinct, impressed 
all across. Hyelobes prominent, ocular fillet faint. Occi- 
pital ring rounded backward. 
Cheeks arched upward in the middle, depressed at the 
posterior furrow. Movable cheek broad, with a rather wide 
marginal furrow and sharp flaring genal spine about as long 
as the inner area of the cheek. Posterior furrow distinct. 
Pygidium nearly semi-circular (longer than half the 
width), with a broad, flat margin. Rachis distinct, extend- 
ing to the marginal furrow, divided into three distinct and 
two or more faint rings; lateral lobes with three furrows. 
