62 PALEONTOLOGY OF THE EUEEKA 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 lirnb. 



This peculiar little species (the head is but 3 mm 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, n. sp. 

 Plate ix, fig. y~. 



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 eye- 

 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. 



