DESCRIPTION OF GENERA AND SPECIES. 289 
marked by about six narrow, faint, grooved segments which reach half-way across 
the slopes. Anteriorly, close to the margin and parallel with it, a subangular groove 
extends from each side of the axis about half-way across the pleural slopes; in front 
of and outside the lateral extremities of these grooves the surface is abruptly 
compressed. 
The dimensions of the type specimen are: approximate length 9 mm., width 
14.5 mm., width of axis anteriorly 4.8 mm., length of axis 7 mm. 
This species is known only from the pygidium, and even that portion is incom- 
plete. It is referred to the genus Megalaspis by reason of the grooved pleural 
segments. The segmentation is very faint and would probably be even less distinct 
or perhaps obsolete entirely were the test of the specimen preserved. 
Illenus ? bronteoides Weller (plate 26, fig. 10). 
1907. Illenus ? bronteoides Weller, Proc. U. S. Nat. Mus., vol. xxxuI, p. 563. 
Pygidium subsemicircular in outline, flattened on top. Axis ill-defined, unseg- 
mented, occupying a little less than one-third the total width of the pygidium ante- 
riorly, very slightly elevated in front and merging into the general surface of the 
pygidium posteriorly. Pleural slopes flattened on each side of the axis, sloping to 
the margins exteriorly with a slightly concave slope. The surface of each pleural 
slope, when the test is removed, is marked by about 12 or 13 very narrow and scarcely 
elevated ribs which are grooved longitudinally and extend from the indefinite axial 
furrows about to the line where the surface begins its more abrupt slope to the lateral 
margins. 
The dimensions of the type specimen are: length 8.5 mm., width 14.8 mm., 
width of axis anteriorly 4.5 mm. 
This species is represented by a single specimen in the collection, a nearly com- 
plete pygidium. It is a peculiar form having the general contour of an Jllenus, 
but with the pleural slopes faintly segmented, suggesting the genus Bronteus. "These 
segments are very faint, however, and would possibly not be visible at all were the 
specimen completely covered with the test. 
Proetus ? sp. undt. (plate 26, fig. 11). 
A nearly complete pygidium is referred with some hesitation to the genus 
Proetus. It is semielliptical in outline,6.5 mm. long, and 8 mm.wide. ‘The surface 
is regularly convex with a concave marginal border, the axis being but slightly ele- 
vated above the pleural slopes. The axis is divided into about twelve segments and 
terminates in a bluntly rounded point just within the marginal border. The pleural 
slopes are marked off by about nine segments somewhat fainter than those of the 
axis, and reach to the marginal border. In some respects this pygidium suggests 
some of the asaphids, but without additional material its true relationships can not 
be certainly established. 
Calymene ? sp. undt. 
A very incomplete pygidium of a trilobite seems to represent a species of Caly- 
mene, although it is too imperfect to allow even the generic identification to be made 
with certainty. 
Pterygometopus ? sp. undt. (plate 26, fig. 12). 
A single imperfect pygidium seems to be referable to this genus. The specimen 
has a well-defined axis with 12 annulations, the pleural slopes being divided into 9 
segments without longitudinal grooves. 
