46 Trans. Acad. Sci. of St. Louis. 
Emmons in being regularly ovate, fifty millimeters long 
by seventy-five millimeters broad, and in the surface be- 
ing plain on either side of the median fold. The speci- 
men figured by HKmmons seems to have been deformed by 
pressure applied from the sides. 
HYOLITHES, N. sp. 
This form differs from H. baconit Whitfield in the ven- 
tral surface being evenly convex instead of subangular. 
The specimens in the collection are too fragmentary 
for description. Number 11532 of the invertebrate pal- 
eontological collection of Walker Museum. 
PTERYGOMETROPUS LINCOLNENSIS, Nl. sp. 
Pl. vu. f. 17-19. 
General form elongate, slender, tapering gradually 
posteriorly. Cephalon subcresentiform, with a com- 
pressed, obtusely angular projection in front. Frontal 
lobe of glabella short and broad, proportion of length to 
breadth about six to seven. First lateral furrows reach- 
ing the dorsal furrows and separating the first lateral 
lobes from the frontal lobe. Inner ends of these furrows 
about two millimeters apart. Second lateral furrows 
very short and deeply impressed at their inner ends. 
First and second lateral lobes confluent at their outer 
ends. Third lobe of glabella very small and not confluent 
with the second lobe. Occipital ring prominent at the 
median line, projecting above the rest of the cephalon. 
It bears no tubercle. Frontal lobe and sometimes the 
first and second lateral lobes sparsely tuberculate. Eye 
elongate, reaching from the outer end of the first lateral 
furrow to the occipital furrow. Posterior part of fixed 
cheek very small and usually not preserved with the spec- 
imens. It bears no genal spine. 
Thoracic segments eleven. Pygidium subtriangular. 
Pleura with eleven or twelve segments, one or two of the 
posterior ones indistinct; axis tapering gradually be- 
hind and reaching nearly to the posterior end of the 
