EURYPTERID^. 
EUllYPTERUS, Dekay. 1825. 
Euryptekus Beecheri. 
PLATE XXVII, FIG. 5. 
Euryptei'us Beeclie>’i, Hall. Second Geol. Surv. Pennsylvania, PPP, p. 30, xil- iii, fig’- 1. 1S84. 
Cephalon unknown. 
Body elongate, broadly convex along the dorsum, becoming more elevated pos¬ 
teriorly ; composed of twelve somites, which gradually increase in breadth 
from the first to the fifth; thence backward rapidly decreasing in width 
and increasing in length, the eleventh having a length equal to one-half its 
width, while the fifth is nearly five times its length. The surface of the 
somites toward the lateral margins is depressed, the margins themselves 
being slightly produced at the postero-lateral angles into mucronate exten¬ 
sions. The posterior dorsal margin of each somite bears a single row of 
triangular scales or tubercles. The number of these scales varies with the 
width of the somite, there being six on the narrower and eight or more 
on the broader somites. 
At the anterior portion of the specimen are preserved two joints of one of 
the great swimming feet, which are remarkable for their length and the three 
or more strong longitudinal ridges upon their surface. The distal joint has 
a length of more than three times its width, and the proximal joint a length 
of nearly five times its width. These joints are probably the fourth and 
fifth, the smaller joints near the base of attachment having disappeared. 
