THE EURYPTERIDA OF NEW YORK 173 
Another interesting specimen is that reproduced on plate 5, figure 
7 which shows two circular, transversely wrinkled patches behind the 
frontal margin. 
Specimens plate 5, figures 3-5, show a trilobation of the abdomen on ac- 
count of the distinct depression of the epimera. It will be noticed that 
the spines on the posterior margins of the tergites are restricted to the 
axis. Where the body is slightly bent, as in specimens figures 3 and 4, 
peculiar oblique folds appear, which indicate the relative thinness of this 
part of the integument and may correspond to folds that formed during 
the life of the animal. This condition gives the test a peculiar trilobite- 
like appearance. 
We have already mentioned among the differential characters of 
-E.remipes and E. fischeri the double series of scales on the dorsal 
side of the postabdomen. In specimens where the inside of this integu- 
ment is exposed, it is seen that between these rows the carbonaceous film 
appears lighter, suggesting a somewhat thinner test, which at the same time 
projects a little. This fact indicates that the interspace marks the position 
of the alimentary canal, the scales being the attachment places of the sus- 
pensory muscle strands. The interspace would then correspond to the 
projecting preanal ridge on the last segment in Pterygotus, which is also 
attributed to the pressure of the intestine. 
Another specimen worthy of notice is one in which the test of the 
carapace is partially weathered, leaving the cast of the interior surface of 
the frontal part exposed and exhibiting a faint radiating structure that is 
restricted to the region where, from analogy with Limulus, the liver must 
have been located. It resembles strikingly the supposed liver impressions 
seen in some trilobites. 
Eurypterus lacustris Harlan 
Plates 9-12; plate 13, figure 3 
Eurypteruslacustris Harlan. Geol. Soc. Pennsylvania Trans. ‘1834. 1: 98, pl.s5 
E. lacustris Hibbert. Roy. Soc. Edinburgh, Trans. v. 13, pl. 12 
E.remipes Bronn & Roemer. Lethaea, 3d ed? 1854. 2: 666, pl. 93, fig. x 
