118 
PALEONTOLOGY OF NEW YORK. 
aiigulated along the axial line, each sometimes bearing a moderately strong 
tubercle. 
PleurcB depressed in a more or less abrupt curve to the margin, bearing- 
eleven or twelve flattened annulations, which are separated by moderately 
strong sulci. Each annulation is faintly grooved by a fine impressed line, 
which is sometimes almost or quite obsolete. Border broad, becoming exca¬ 
vate and slightly reflexed posteriorly; all the annulations except two becom¬ 
ing obsolete upon reaching it. 
Doublure broad, reaching to the termination of the axis. 
Surface Ornamentation. The cephalon is covered with low tubercles which 
become obsolete upon the anterior portion of the glabella and the depressed 
areas of the cheeks. Upon the thorax and pygidium each segment and 
annulation is ornamented with granules; these upon the latter sometimes 
appear to be arranged in two rows, one upon each limb of the pleural annu¬ 
lations. In rare examples a row of small tubercles is noticeable along the 
axial line on both thorax and pygidium, beginning with a faint tubercle upon 
the occipital ring, the next being at the third or fourth segment, thence 
backward becoming stronger toward the apex of the axis. 
Dimensions. An average individual measures : 
Body. Cephalon. Thorax. Pygidium. 
Length_ 37 mm. 13 mm. 11 mm. 13 mm. 
Width__ 24 mm. 24 mm. 22 mm. 21 mm. 
Tlie largest entire individual observed has a length of 60 mm. and a width 
of 40 mm. 
Observations. Entire individuals of Proetus macrocephalus are of rare occur¬ 
rence, and the crust is so delicate and tenuous that when the parts are in 
juxtaposition, it is usually broken away. The symphysis along the fiicial 
sutures appears to have been very free, for the movable cheeks are usually de¬ 
tached, and of several hundred specimens of the species which have passed 
under observation but a single example retains all the parts. 
