THE EURYPTERIDA OF NEW YORK 57 
bisegmented structure in the metastoma, indicating that it originated 
from a paired organ. He considers it homologous to the chilaria of 
Limulus, a pair of movable sclerites set behind the coxal segments of the 
last pair of legs [text fig. 10] and remarks that the metastoma of 
the eurypterids certainly represents a much higher development of the 
organ than the chilaria of Limulus. Pocock [1g01, p. 302] considers the 
metastoma as the homologue of the sternum of the scorpion but the obser- 
vations of Kishinouye [1891] upon the embryo of Limulus longi- 
spina and those of Brauer [1895] on the embryo of the scorpion demon- 
Figure 13. Eurypterus fischeri Fich- Figurerg Eurypterus fischeri Eichwald. 
wald. Endostoma, seen from below (out- On ‘the left the right coxa, seen from the in- 
side). (From Holm) terior and showing the doublure, the large 
cutting tooth and the smaller teeth; and its 
connection with the metastoma (on the right), 
which also shows its interior doublure. (From 
Holm) 
strate that it represents the appendages of a distinct suppressed segment. 
For practical reasons we have not counted this abortive first segment of 
the preabdomen [see diagram p. 24]. 
Gaskell, in his lately published The Origin of Vertebrates, in order to 
derive a vertebrate prosomatic or oral chamber fully separated from the 
gill chambers, has assumed that the metastoma and the operculum of 
Eurypterus became fused [op. cit. p. 242 and our text fig. 16]. Itis safe 
for us to say that we have no evidence in the eurypterids of any tendency 
toward the fusion of these organs and that it seems to us such a procedure 
