192 PALEOZOIC PALEONTOLOGY. 
the impression of the wide, punctured, marginal border of the head, 
these specimens being similar to the one illustrated by Clarke from 
Minnesota. 
TRINUCLEUS CONCENTRICUS (Eaton). 
Plate XIV., Figs. 3-4. 
1847. Trinucleus concentricus Hall, Pal. N. Y., vol. L., p. 249, pl. 
65, figs. 4 a-c. 
Description—Head semi-circular or subcrescent-form in outline, 
the genal angles either destitute of spines or produced into long, 
slender, straight spines. Glabella smooth, very prominent, ovoid in 
outline, the widest portion being in front, with a short, blunt spine 
posteriorly; cheeks smooth, prominent, but depressed considerably 
below the glabella, from which they are separated by a well-defined 
dorsal furrow; eyes wanting. The entire anterior and lateral margins 
of the head are surrounded by a broad, somewhat flattened or concave 
border, which is marked in front by from three to five concentric rows 
of deep, rounded pits; one or two additional rows are introduced on 
the sides, and toward the genal angles the pits often become irregularly 
scattered. 
The thorax and pygidium have not been observed in New Jersey. 
The dimensions of one of the best specimens observed, a nearly-com- 
plete head, are: length, 10 mm.; width, 15 mm.; convexity, 6 mm. 
ISOTELUS GIGAS De Kay. 
Plate XIV., Figs. 5-7. 
1824. Isotelus gigas De Kay, Ann. Lyc. Nat. Hist., N. Y., vol. I, 
play pl dei ale pl elSs seals 
1847. Isotelus gigas Hall, Pal. N. Y., vol. 1, p. 231, pl. 60, figs. 
7 aH, pl. 61, figs. 3 a—m, 4 a-c, pl. 62, figs. 1 a—c, 2, pl. 63. 
189%. Isotelus gigas Clarke, Pal. Minn., pt. II., p. 701. 
Description—Outline of an entire individual subelliptical, with 
the anterior and posterior extremities somewhat pointed; the triloba- 
