220 NEW YORK STATE MUSEUM 
pressions of the opercular appendage; especially distinct 1s that of the 
anterior hastate part. 
The ornamentation of the dorsal side is very striking. The carapace 
is for the most part smooth, but on the middle posterior region there 
appear small prominent tubercles most of which are semilunar and project 
backward. They are irregularly crowded around a median smooth de- 
pression. Along the posterior margin the semilunar scales are abruptly 
changed into two rows of larger, sharply angular scales. The first tergite 
is smooth; the following tergites as well as the postabdominal segments 
show a dense mass of extremely small semilunar to linear scales on the 
anterior half (mostly of so small size that these parts appear smooth), while 
the middle posterior halves bear prominent angular scales that are largest 
upon the median nodes. Toward the sides the angles of the scales become 
smaller until linear scars are formed, making a system of parallel oblique 
lines on the epimera (not well shown in the figures). 
Measurements. The carapace is 32 mm long and approximately 53 mm 
wide at the base. The eyes were 5.5 mm long and 16 mm apart. The 
preabdomen measures 46xX62.5+mm. The first tergite is 4 mm long; 
the second 7.5 mm long and 59 mm wide; the third is 9.5 mm long and 
61+ mm wide. The first postabdominal segment measures 9 kK 52 mm, 
the next 11.5x26+mm. The limbs are only fragmentary. 
Horizon and locality. Lower Coal Measures of Mazon Creek, Grundy co., 
Illinois. Counterpart in American Museum of Natural History (no. 8532). 
Genus EUSARCUS Grote & Pitt 
The most striking and interesting eurypterid of the waterlimes of 
Buffalo is undoubtedly a large animal which, when discovered in 1875, 
was made the type of a new genus and species by Grote and Pitt under the 
designation.of Eusarcus scorpionis. The authors of the genus 
gave no generic diagnosis but the following description of the species 
suggests what they considered as its distinctive characters: 
The cephalothoracic portion appears to be separate from the body, 
and to be considerably narrower in proportion than in allied forms. The 
