THE EURYPTERIDA OF NEW YORK 223 
' Eurypterus (Anthraconectes) mazonensis Meek & Worthen 
Plate 26, figure 1 
Eurypterus (Anthraconectes) mazonensis Meek & Worthen. Am. 
Jour. Sci. & Arts. 1868. 46: 21, figure 
Eurypterus (Anthraconectes) mazonensis Meek & Worthen. Geol. 
Sur. Illinois. 1868. 3: 544, figure 
Eurypterus (Anthraconectes) mazonensis Hall. Pennsylvania 
ad Geol. Sur. Rep’t of Progress, PPP. 1884. p. 25, fig. 2, 3 
Meek arid Worthen have elaborately described and illustrated by an 
outline sketch this species from the iron stone concretions of the Carbonic 
of Mazon creek, Illinois. T heir material consisted of but one specimen 
which exhibits the ventral side. Professor Whitfield kindly pointed out 
to us that the counterpart of this type is in the American Museum of Nat- 
ural History and this has been made accessible for our study. The latter 
is a well preserved intaglio which happily complements the type. We 
therefore embrace this opportunity to add such data to the knowledge of 
this curious species as are furnished by this specimen. The most remark- 
able of these is the strong contraction of the postabdomen. 
The excellent photograph! reproduced on plate 26, figure 1 shows 
the condition of the specimen and all essential features observable in 
it. Some structures, as the position of the eyes, the outline of the impression 
of the opercular appendage, are only observable with favorable illumination. 
It has been possible to demonstrate the outlines of the carapace and first 
tergites a little better than shown in the photograph. These features as 
well as the outlines of the doublures of the tergites are illustrated by a 
text figure. For the sake of completeness we have also copied the outline 
drawing of the ventral side, given by Meek and Worthen. 
Description. Body long, elliptical in outline, with the posterior 
third truncated by the abrupt contraction of the postabdomen. It is 
widest in the region of the fourth tergite, increasing gradually from the 
1 A drawing of this counterpart was given by Hall loc. cut. 
