46 
PALEONTOLOGY OF NEW YORK. 
of a considerable variation in size, from a length of 5 mm. to a length of 
120 mm., as indicated by a large fragment, and this development in indi¬ 
vidual growth is accompanied, in the earlier stages, by considerable variation 
in the form of the pygidial lobes. A pygidium measuring 1 mm. in length 
and 3 mm. in width to the tips of the spines, has a very elevated axis, which 
is snb-spinose along the axial line, strongly incurved toward the extremity, 
and bears but six annulations. The marginal spines are unusually elongate 
and baccillate, the first pair being longest, the length decreasing backward, 
the two posterior pairs becoming strongly incurved toward the posterior 
extremity. The terminal lobe is very small and scarcely visible. With 
advancing growth the spines become relatively broader, and radiate regularly 
from the curve of the margin, assuming a sub-equal length, and the terminal 
lobe becomes gradually more conspicuous. Individuals occur occasionally in 
the shales of tlie Hamilton group, which indicate a slight inclination from 
the type of Dalmanites {C.) Boothi to that of the variety D. (C.) Calliteles to the 
extent of retaining the broad, short, vertically flattened cheek-spines of D. (C.) 
Boothi, and showing a tendency in the thoracic segments to become spinose 
on the axis, and in the pygidial spines to become narrow and acute. Such 
forms would naturally be expected in abundant material, but their rare 
occurrence, makes it inadvisable to recognize the usual variation as a dis¬ 
tinct specific form. 
Dimensions. A normal adult of Dalmanites {Cryphceus) Boothi affords the 
following measurements: 
Body. 
Cephalon. 
Thorax. 
Pyg-idium. 
Length _ 
_ 38 mm. 
12 mm. 
16 mm. 
11 mm. 
Width_ 
. 24 mm. 
24 mm. 
22 mm. 
18 mm. 
Of Dalmanites {Cryphceus) Boothi, var. 
Calliteles, the following: 
Body. 
Cephalon. 
Thorax. 
Pygidium. 
Length_ 
_ 37 mm. 
13 mm. 
13 mm. 
11 mm. 
Width_ 
_ 26 mm. 
26 mm. 
19 mm. 
21 mm. 
