THE EURYPTERIDA OF NEW YORK 301 
Description. Carapace subrectangular, its length and width approx- 
imately as 2:3; both the anterior and posterior angles approaching right 
angles in older specimens; anterior angles, however, more rounded than 
the posterior ones. Frontal margin varying in different specimens from 
slightly convex to gently emarginate; lateral margins moderately convex, 
posterior margin broadly concave. The greatest width is found in the 
middle between the anterior and posterior margins. The upper test carries 
but a very narrow thickened rim on the anterior and lateral margins; it is 
continued, however, into a very broad, concentrically furrowed doublure 
on the underside, which in front attains one sixth the length of the cara- 
pace and becomes reduced to one half that width toward the genal 
angles. The eyes are very large (one third of length of carapace); much 
elevated, furnished with a semicircular, narrow visual area; approx- 
imate, about their own length apart, situated a little forward of the bi- 
secting line. The ocelli are situated on a prominent, heart-shaped mound 
between the posterior extremities of the lateral eyes. The surface is covered 
with closely arranged prominent tubercles which along the frontal margin 
are arranged in concentric rows. 
The first tergite is short and wide and like the following furnished 
with a row of large tubercles along the posterior margin. 
Measurements of type [first specimen figured, 1907, vl. 6, fig. r]. — mitlimeters 
Length of carapace... ..... eee ee eee 12.3 
Width 0... cee 16.5 
Width of doublure.........0.0.. 0000.00. eee I.5+ 
Length of lateral eve...... 00... ee 2.5 
Distance between visual surfaces.................... eee QQ. 
Exposed length of first tergite.................... ee. 1.2 
Width .. 0... eee een tele. 12.4 
The smallest carapace observed measured 
Length of carapace... 2... eee eee nes 3.5 
Width 0... ccc eee nee fo cee eee 5.5 
Length of lateral eye..... eee ee eee es 
Distance between visual surfaces...................0..00. 4. 
