BOOK 2) PALEOZOIC PALEONTOLOGY. . 
from this species in the more angular outline of the head, the more 
prominent eye-lobes, the flattened dorsal surface and the much broader 
occipital ring. Our species also occurs at a somewhat lower horizon 
than those from Minnesota, being in the Black River horizon of the 
Trenton limestone as it occurs in New Jersey. 
PLATYMETOPUS TRENTONENSIS (Gon.). 
Plate XV., Figs. 17-19. 
1842. Asaphus? trentonensis Con., Jour. Acad. Nat. Sci. Phil., vol. 
WIE peri 7, plemiosis.! 10: 
1847. Platynotus trentonensis Hall, Pal. N. Y., vol. L., p. 235, pl. 
64, figs. 1 a-d (not 1e). 
1897. Platymetopus trentonensis Clarke, Pal. Minn., pt. II., p. 753. 
Description.—Head ventricose, the curve along the median line 
from the posterior to the anterior margins being very nearly a semi- 
circle, subsemi-circular in outline, attaining a breadth of 35 or 40 
mm. The glabella very large, occupying nearly the entire breadth 
of the cranidium, strongly protuberant in front; with a single pair 
of glabellar furrows, which originate at the anterior, lateral mar- 
gins, and, after curving inward, then backward and then slightly 
outward again, forming something more than a semi-circle, they join 
the occipital furrow, dividing the glabella into three lobes; the 
frontal or median lobe is broad in front, becoming narrower pos- 
teriorly to a point back of the middle of the head, and then again 
broadens out, becoming nearly as wide on the occipital furrow as 
it was on the anterior margin; the two lateral lobes about as promi- 
nent as the median lobe, subcrescentiform in outline. Dorsal furrows 
concave inward, about as deeply impressed as the glabellar’ fur- 
rows. Fixed cheeks rather broad along the posterior margin of the 
head, becoming rapidly narrower to a point just behind the pal- 
pebral lobe; the palpebral lobe rather prominent, the cheek becoming 
very narrow anteriorly. Occipital furrow and occipital segment well 
defined, extending across the fixed cheeks. The entire surface orna- 
mented with small, low, rounded tubercles, somewhat variable in size. 
Free cheeks, thorax and pygidium unknown. 
