EURYPTEH/IDA 

 EURYPTERID.E. 



EURYPTERUS, Dekay. 1825. 



EURYPTERUS BEECHERI. 



PLATE XXVII, FIG. 5. 



Elirypterus Beecheri, Hall. Second Geol. Surv. Pennsylvania, PPP, p. 30, pi. iii, fig. 1. 1S84. 



Cephalon unknown. 



Body elongate, broadly convex along the dorsum, becoming more elevated pos- 

 teriori v ; 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 live times its width. These joints are probably the fourth and 

 filth, thi' smaller joints near the base of attachment having disappeared. 



