70 NEW YORK STATE MUSEUM 
the new features that lead to Stylonurus and Erettopterus. In Euryp- 
terus also the telson has still the original four-sided form, but the two upper 
sides have already become so reduced that they are united in either a flat 
or a concave broad dorsal side, while the ventral edge is developed into 
a flat-topped carina.t In Hughmilleria the development is reversed, the 
dorsal side bearing a carina, and the ventral side being smooth and either 
flat or but shghtly convex, the telson having thus the subtriangular section 
and dorsal carina of that in Limulus. The essential characters of the telson 
of Eurypterus are retained in Dolichopterus. In Anthraconectes, however, 
it becomes extremely long and styliform, thus assuming the characters in 
Drepanopterus and Stylonurus. In the extreme forms of the latter genera 
the telson becomes contracted in the proximal portion and expanded 
clublike in the distal portion, sometimes with development of flat lateral 
carinae or flanges, asin Stylonurus scoticus. 
The telson of Eusarcus was apparently still four-keeled; but it was 
bent downward toward the end, so that when the scorpionlike tail was 
thrown forward over the body, its sharp point would be directed upward. 
This is an aberrant development of the telson not found in other genera, 
but clearly connected with that of Eurypterus. 
From the telson of Hughmilleria first that of Slimonia, and through > 
the latter, those of Pterygotus and Erettopterus can be derived. Slimonia 
possesses a long tail spine with dorsal carination. The anterior portions 
of the lateral carinae of this spine, however, are developed into two broad 
flanges which together form an oval, leaflike expansion with coarsely serrate 
posterior margin, the median keel being continuous with the long spine 
[see text fig. 25]. In Pterygotus the projecting spine of the Slimonia 
stage has been reduced to the size of the serrations of the flanges, and 
in Erettopterus the reduction of the median spine that has become the 
axis of the broad leaflike telson has been carried still further so that a 
bilobed telson has resulted. 
The keeled lateral and ventral edges of the tail spine in Eurypterus 
and the lateral edges of the broad telson in Pterygotus and Erettopterus 
‘It is possible that this section is but the result of compression and desiccation 
and that the living specimens had a trapezoidal section. 
