WATERLIME GROUP. 
411 * 
This species lias been referred to E. l-acustris , and the resemblance is very close. 
The form of the anterior feet and the swimming feet are essentially the same, while 
the joints of the body are proportionally longer and stronger; furnishing sufficient 
ground for a variety, but not satisfactory evidence of specific_difference. 
Fig, 1. View of the specimen from the lower side. 
Geological position and locality. In the Waterlime group, near Buffalo. 
Earypterus dekayi (n. s.). 
Plate LXXXII. Fig. 1. 
Carapace semicircular, length being to the width as 11 to 19, anteriorly 
and laterally margined by a slightly elevated rim. Body broad, ovato- 
lanceolate ; length, including the tail-spine, a little more than twice 
and a half the greatest width; width across the thorax greater than 
the base of the head, gently narrowing at the fifth and sixth segments, 
and below this more abruptly contracted. The first six segments are 
plain, and rounded at their lateral margins; those below are imbricate 
with mucronate extensions, while the last one is alate on each of its 
lateral edges, and is extended at its posterior angle in mucronate or 
spiniform processes over the base of the tail-spine. The abdominal joints 
gradually increase in length to the eleventh, and the twelfth is twice 
as long as the preceding. The tail-spine is triangular, as long as the five 
preceding joints, and, in its present condition, concave along the upper 
side, with the angles apparently free from serrations. 
Postoral plate suboval, greatest width a little above the middle, the an¬ 
terior end concave. The pairs of feet originate a little anterior to the 
middle of the carapace : the basal joints are short; the maxillary 
plates broad and strong; the coxa is wide and short (the succeeding 
joints are not discernible in the individual) : the fourth, fifth, and 
sixth joints have their distal angles strongly mucronate ; the seventh 
joint is abruptly dilated, comparatively broad and short, while the 
movable chela is likewise short and broad, and the terminal palette 
small. The central thoracic appendage reaches to the fourth articulation, 
with the terminal processes short. 
