THE EURYPTERIDA OF NEW YORK 55 
walking legs of Eurypterus, but those of the first pair of somewhat dif- 
erent appearance and therefore possibly belonging to a different category 
of structure. We have also observed this appendage [see text fig. 12; 
pl. 57, fig. 3]. | 
The coxa of the fifth pair differs in structure and size from those 
of the preceding legs. It corresponds in its large size to that of the entire 
leg which surpasses all other limbs in dimensions. It is of rhom- 
boidal form, with a large neck on the anterior inner angle forming the 
gnathobase. The manducatory edge [pl. 72, fig. 2] 1s made up 
of an upper sharp cutting portion and a lower crushing portion con- 
sisting of a row of teeth which as a rule become finer posteriorly. The 
neck often becomes so lengthened as to give the coxa a retortlike appear- 
ance, as in Hughmilleria and Pterygotus and especially so in Dolichopterus 
and Eusarcus, where the necklike extension becomes as long as or longer 
than the rhomboidal base. This great extension of the gnathobase in 
the latter two genera is clearly correlated to the great longitudinal exten- 
sion of the cephalothorax and the forward position of the mouth. In Hugh- 
milleria, Pterygotus and especially Slimonia, the similarity to a retort is 
still much increased by the rounding outline of the body of the coxa. In 
Dolichopterus and Eusarcus the immense last coxae cover more than 
half of the ventral side of the cephalothorax [pl. 44]. Their form is 
quite characteristic in the different genera and the generic relations of 
detached coxae are readily recognized. While the large last coxa covers 
the preceding coxal segment as well as the anterior portion of the first ventral 
abdominal segment or operculum, the inner portion, except the chewing 
edge, is in turn covered by the underlip or metastoma. 
The mouth, which is situated at about the middle of the ventral side 
of the carapace, is surrounded not only with the coxae but also by 
several covering liplike plates. One of these is the eptstoma of Ptery- 
gotus. This was first described and figured by Huxley and Salter [Monogr. 
pl. 1, fig. 1]. They were, however, misled, probably by the direction 
of the sculpture on it, and figured it with the straight margin toward 
