. 
: SILURIAN FAUNAS. 249 
flattened border being smooth within, but toward the margin covered 
with fine, raised tubercles and elongate flexuose markings. 
The dimensions of an average-sized pygidium are: length, 10 mm. ; 
width, 13 mm.; and convexity, 4.5 mm. A rather small head is 7 
mm. long on the median line and probably 11 mm. wide, but some 
fragmentary specimens must have been more than twice this size when 
complete. 
Remarks.—Fragments of the head and pygidium of this species are 
not wncommon in the coralline layer at the Nearpass cliff. The 
species was first recognized and named by Dr. Barrett, but no proper 
description of it was ever given. 
PROETUS? DEPRESSUS 0. Sp. 
‘Plate  OXeNGe ics 2ie 
Description Known only from the pygidium, which is semi-cir- 
cular in outline. The axis is depressed, about five-sixths the total 
length of the pygidium, with about ten segments; occupying one-third 
the width of the pygidium anteriorly, tapering rather abruptly pos- 
teriorly, where it is bluntly rounded, the lateral, bounding furrows 
continuing indefinitely to the posterior margin of the pygidium. 
Plure flattened adjacent to the axis, convex toward the border, with 
a slight, concave furrow within the convex marginal border; marked 
by six grooved segments on each side, the grooves being located cen- 
trally and being fully as deep as the furrows between the segments, but 
not extending across the marginal border. The bounding furrows of 
the segments are continued as faint, ill-defined grooves across the 
marginal border. 
The dimensions of the largest and best specimen observed are: 
length, 5.5 mm., and width, 9 mm. 
Remarks.—This species, so far as it has been observed, resembles 
Proetus protuberans Hall, from the Coeyman’s limestone of the Hel- 
derbergian period. The Decker Ferry specimens differ from P. pro- 
duberans in having a less conspicuous marginal border and in having 
a larger number of segments on both axis and plure of the pygidium. 
