412 * 
PALAEONTOLOGY OF NEW-YORK. 
This species differs conspicuously from all the others, in many points of impor¬ 
tance. The entire body is proportionally shorter, the carapace shorter and broader, 
than in E. remipes , and less contracted than in E. lacustris. The swimming feet are 
shorter, and the terminal palette a little more developed than in E. remipcs or E. 
lacustris and the upper abdominal joints differ less from the thoracic joints in 
length, while the last one is alate on the two lateral edges, a feature not observed 
in any other species. The tail-spine is concave above for its whole length, with a 
little triangular elevation in the middle at the base. This concavity may perhaps be 
the effect of pressure, but no other species has shown a similar feature. The absence 
of serrations may be due to the exfoliation of the crust. The entire animal is more 
compact, and all the parts are shortened, with the proportions expressive of great 
force and strength. 
A single specimen of this species only has been observed. 
Pig. 1. The individual, natural size, with the dorsal side upwards. One side has been broken 
off; and this portion, with the swimming foot, is restored in outline, the same 
organ on the left side being essentially entire. The upper part of the carapace 
and the first joints are removed, so as to show the maxillary plates, the postoral 
plate and the bases of the anterior feet, which are broken off so as not to extend 
beyond the margin of the carapace. The thoracic appendage is shown in its 
junction with the first ventral joint, and extending to the base of the fourth joint. 
Geological position and locality. In the Waterlime group at Blackrock, New-York. 
Eurypterns pachyclieirus (n. s.). 
Plate LXXXII. Pig. 1-3. 
Carapace unknown. Body robust: crust thick; articulations strong, those 
of the abdomen extended in strong salient angles at the lateral edges. 
Bases of the anterior feet strong and broad. Swimming feet strong and 
large; the seventh [sixth] joint very large and long, inflated and much 
curved on the anterior side : the free eighth joint is thick and strong, 
somewhat oval, and narrowing gently towards the point of articulation; 
the terminal palette is small. The last joints (and perhaps the others) 
of the swimming feet are serrated on the margins. 
No entire specimens of this species have been seen, and the description is drawn 
from an imperfet specimen preserving eleven articulations of the thorax and abdo¬ 
men, measuring altogether five and a half inches in length, and three and a quarter 
inches the greatest width. On the same specimen are preserved some fragments of 
the carapace, the bases of the feet, parts of the maxillary plates, and a joint of the 
