THE EURYPTERIDA OF NEW YORK 335 
_ Hughmilleria socialis Sarle 
Plates 59-53 
Hughmilleria socialis Sarle. N. Y. State Palaeontologist Rep’t. 1902. 
p. rogt, pl. 6-9; pl. 10, fig. 1-6, 8, 9; pl. 11-14; pl. 15, fig. 4-6; pl. 24, fig. 1; pl. 25, 
fig. 1, 3, 4; pl. 26, fig. 3, 5 | 
This is by far the most common eurypterid in the Pittsford shale 
and is the genotype and best known species. It has been as elaborately 
described by Sarle as its novelty, its singular features and the excellence 
of the material deserve. The original description is as follows: 
This type is comparatively small, the length of the average individual 
not exceeding 15 cm. Viewed from either the dorsal or the ventral side, 
the outline is slenderly lanceolate. In the natural, undistorted condition, 
the anterior part of the body is flattened, the dorsal and ventral surfaces 
being slightly convex, while the caudal portion is nearly cylindric. 
Cephalothorax. ‘The cephalothorax is semielliptic or subtriangular in 
outline, the length equaling the breadth at the base, and comprising about 
one fifth the length of the entire body. Along the gently curving sides 
and acutely rounded front is a narrow flattened border, striated on the 
under surface, and not exceeding a fraction of a millimeter in breadth. 
The dorsal surface is slightly rounded or arched from the side to the center, 
so that in an undistorted shield 22 mm long, the elevation is about 2 mm. 
The posterior edge, except for a slight forward curve at the genal angles, 
is straight. The compound eyes barely break the outline of the shield: 
they are small, elongate, widest anterior to the middle, the outer side 
arcuate, the inner formed by three nearly straight edges—a short basal 
and a little longer anterior, forming slightly rounded obtuse angles with 
a long inner side. The anterior end of the eye is acute. The length of 
these organs on the cephalothorax, the dimensions of which were given 
above, is 5mm. However, the usual proportion between the length of the 
shield and eye is as 1: 4.5. A line drawn connecting the posterior ends 
of the eyes passes through the center of the shield. The ocelli are 
situated on a small tumescence cut by this line; they form two minute, 
ringlike prominences separated by about the length of their diameter. 
Abdomen. The abdomen, at the widest point, or between the third 
and fourth dorsal segments, is a little wider than the base of the cephalo- 
thorax. Thus, in one animal measured, these dimensions were respec- 
tively 24 mm and 17.5 mm, in a second 23 mm and 17 mm, and in a 
