62 PALEONTOLOGY OF 'THE EUREKA DISTRICT. 
the fixed cheeks; postero-lateral limbs strong, extended laterally and with 
a distinct marginal furrow, which is usually the continuation of the occipital 
furrow. Facial suture directed gently forward from the eyelobe towards 
the front, recurving to the frontal margin of the head so as to round the 
lateral angles of the frontal limb; behind the eye it passes to the posterior 
margin at an angle of 20°-25° with the latter, outlining a triangular-shaped 
lateral limb. 
This peculiar little species (the head is but 3"™ in length) appears to 
unite some embryonic features with those of the adult individual. It is 
doubtfully referred to Agraulos. The discovery of allied species or more 
specimens of this one may enable the observer to determine more fully its 
true generic relations. 
Formation and locality—Cambrian. In a small outcrop of limestone on 
the west side of the Eureka District, Nevada. 
Genus ARETHUSINA Barrande. 
Arethusina Americana, 0. sp. 
Plate ix, fig. 27. 
Glabella and fixed cheeks united, a little wider than long, the front 
broadly rounded, and the sides a little contracted midway. Glabella promi- 
nent, conical, convex, rounded in front, and marked by two pairs of short 
furrows extending obliquely inward less than one-fourth the distance 
across; occipital ring narrow, defined by a shallow occipital furrow; fixed 
cheeks broad, sloping away from the well-defined dorsal furrows to the 
minute palpebral lobes; well-marked ocular ridges cross from opposite the 
anterior portion of the glabella to the eyelobes; all in front of these is 
occupied by the broad, expanded frontal limb; it is slightly convex to the 
anterior narrow marginal rim; postero-lateral limbs but little extended lat- 
erally and with a marginal groove within the posterior border. Facial 
suture extends a little outward in a gentle curve to the frontal margin from 
the eyelobe, recurving just before reaching the margin; behind the eys- 
lobe it is directed obliquely backward, outlining a triangular lateral limb 
and cutting the posterior margin at a distance from the dorsal furrow equal 
to the width of the glabella at its base. 
