AN EURYPTERID HORIZON IN THE NIAGARA. 
9 
and (probably from this cause) have two longitudinal grooves 
dividing the area into three parts, the centre containing one-half and 
the sides each one-quarter of the total area. The proximal ends of 
some specimens are enlarged and rounded, indicating a well form- 
ed joint with the distal, post-abdominal segment. 
The spines from the ectognathites or walking legs measure 
1*7 to 3 • 5 cm. in length, 0 * 35 to 0 • 5 cm. in width at mid-length, 
and 0*4 to 0*6 cm. in width at the joint. 
These spines are nearly straight, the thicker edge being 
convex and projecting slightly beyond the thinner edge, which 
is gently convex near the proximal end and resupinate near the 
point. In one specimen the joint is considerably enlarged and 
thickened. The spines, although crushed to some extent, 
appear to have been very thin. 
The manducatory edges of the gnathobases of the swimming 
legs occur plentifully and in a fair state of preservation. The 
rows of teeth measure nearly 1 cm. in length and are made up 
of 5-6 conical cusps which vary from 2 • 5 mm. at one end of the 
row to less than 1 mm. at the other end. Both the line through 
the bases of the cusps and the line along their crests are concave. 
The metastoma is represented by a fragmentary plate which, 
however, shows the “broad and short, subtriangular” shape 
characteristic of Eusarcus . At its widest part, it is 1*1 cm. 
and at the narrowest part 0*8 cm. wide, the fragment being 0*8 
cm. long. 
Other plates occur which have not been identified with 
certainty. Their surfaces are covered with fine pits. 
I have referred this species to the genus Eusarcus on the 
following evidence: the broad, short, subtriangular shape of 
the metastoma; the number and large size of the spines of the 
walking legs; and the indicated enlargement of the abdomen. 
Logani differs from other species of Eusarcus in the pro- 
portionately great size of the spines and telson. From E. 
scorpionis this species differs also in having a straight ensiform 
telson. 
