122 PALEOZOIC PALEONTOLOGY, 
plure convex near the axis, but becoming flattened or broadly con- 
cave near the margin, with five, or, in the larger specimens, six, dis- 
tinct grooved segments. 
Remarks.—This is by far the commonest trilobite in the fauna at 
Newton, it being represented by fragments of a hundred or more 
individuals in the collection. ‘These vary greatly in size, the smallest 
pygidium being not over 4 mm. in length, while the largest one ob- 
served, when complete, could not have been less than 30 mm. in 
length. The fragments of heads which have been observed also indi- 
cate a great variation in size; several fragments which, however, can- 
not be certainly determined as belonging to this species because of 
their imperfection, must have been portions of a trilobite head which, 
when complete, could not have been less than 50 mm. in breadth. 
All of these fragments of both heads and pygidia which are perfectly 
enough preserved for generic identification seem to belong to a single 
species. 
Among the free cheeks observed, a considerable variation in the 
length of the genal spine is exhibited. The longer spines observed 
must have been equal to the length of the heads of which they were 
a part, and are extended into a very slender point posteriorly. The 
shorter spines have blunter, rounded points, and may simply indicate 
that the terminal portion has been broken away. 
The species most closely resembles D. pepinensis Owen, from the 
Potsdam sandstone of Wisconsin, but differs from that species, espec- 
ially in the pygidium, which, in D. pepinensis, is nearly semi-elliptical 
in outline, with a much more pointed axial lobe. The species differs 
from D. hartit Wale., described from the upper Cambrian limestone 
of Saratoga county, New York, in the anterior convergence of the 
sides of the glabella and in the different shape of the pygidium, which, 
in D. hartu, has the anterior margin curving backward laterally to 
such an extent that the outline of the whole pygidium is nearly 
elliptical. The axial lobe of the pygidium of D. harti is also much 
more pointed than in the species under consideration. The pygidium 
of D. newtonensis resembles that of D. devinet Bill., but the head is 
quite different. The pygidium also resembles that of a species illus- 
trated, but not named, by Hall in Foster and Whitney’s Report on 
the Lake Superior Land District, pl. 23, fig. 3 e. 
_——_——_—— 
