48 NEW YORK STATE MUSEUM 
b Postoral appendages. Of the five pairs of postoral limbs which are 
frequently designated as endognaths or endognathites, the first and fifth 
show the greatest amount of differentiation, while the intervening 
three pairs, as a rule, are very much alike and are functionally uniform, 
mostly serving as walking legs. We find the same condition in both Limulus 
and the scorpions and may therefore infer that the intermediate legs retain 
the original condition and that differentiation most easily affected the 
most exposed pairs, the first and last. 
Generally all legs increase in length regularly from in front backward. 
This condition is typically shown in the more primitive genera Drepanop- 
terus, Eurypterus and Hughmiulleria. 
The legs of Drepanopterus [pl. 54] exhibit the least differentiation 
of all genera, whose legs are known. All five pairs form a series of limbs 
which increase in length backward and are very much alike. One dis- 
tinction, however, is that the first three are provided with a pair of 
fairly large spines on each segment, the posterior being longer than the 
anterior, an arrangement which was obviously of great assistance in 
pushing the body forward. The spines become gradually reduced back- 
ward in the series of legs; in the third pair posterior spines only are 
still well seen, the anterior ones being reduced to mucros. On the last 
pair they are all reduced to mucros. From the legs of Drepanopterus 
those of Stylonurus can be directly derived. 
In Hughmilleria the first four pairs form continuous series of walking 
legs, all four being equally spiniferous and undifferentiated. 
In Eurypterus the structure cf the legs has been most minutely de- 
scribed by Schmidt and Holmin E. fischeri, and our large collection 
of E. remipes and lacustris corroborates their excellent work. 
The first three pairs are thick and heavy and increase in length regularly 
backward. The first leg consists of seven, the second and third of eight 
segments each, the terminal claw included. They are convex on the 
upper and flat on the underside and so articulated that they can be bent 
only downward. The principal spines are articulated and paired, the 
