56 NEW YORK STATE MUSEUM 
the front. Schmidt [1883, p. 71] described it as a subquadrangular plate 
with convex anterior and concave posterior margin, lying directly in front 
of the mouth and a part of the doublure of the carapace, separated from 
the remainder by two sutures. Laurie [1893, p. 516] has shown that 
the scale markings on the epistoma have their convex side directed for- 
ward contrary to the almost universal rule among eurypterids and that 
this fact would seem to indicate that we have here a portion of the carapace 
bent over. At the same time he remarks that some of his specimens are 
fractured along quite different lines than those Schmidt observed. One 
of these he reproduces on plate 2, figure 10. On another [his pl. 1, fig. 4] 
the “‘epistoma ” of Slimonia is reproduced.. This, however, is but the 
ventral marginal plate of the cephalothorax that occupies the space between 
the doublure of the carapace and the thin membrane surrounding the 
coxae and which is termed the ‘‘ Randschild” by Holm. This plate 
in Eurypterus had been figured by Hall [pl. 80A, fig. 12] as ‘‘ the lower 
surface of one side of the cephalic shield”? and has been more fully 
described above. We reproduce in plate 74, figure 3 a well preserved 
upper lp or epistoma of P. macrophthalmus. 
The term endostoma has been applied by Holm [op. cut. p. 28] to a 
small plate that bounds the posterior portion of the mouth. It is here 
figured from Pterygotus buffaloensis [plate 81, figure 4.] 
It corresponds to the promesosternite of Limulus or of the scorpion 
group. To its anterior edge a thinner membrane is attached which passes in- 
ward in the direction of the throat and forms, therefore, the lower lip. 
The metastoma or postoral plate is a highly characteristic organ of the ~ 
eurypterids. “It is large, somewhat variable in form but all its varia- 
tions are derivable from the oval form seen in Eurypterus. Its size 
corresponds to the longitudinal extension of the last pair of coxae since 
it covers their inner margins and the interspace between them. Its frontal 
margin is always more or less emarginate, its margin bent under into a 
broad doublure connected with the membrane covering the interspaces 
of the ventral side. Holm has shown that there are traces still present of a 
