136 NEW YORK STATE MUSEUM 
limulids, and may here briefly enumerate them. The nepionic stages of 
both have in common: 
1 The large size of the carapace 
2 Its broad border : 
3. Its distinct median, glabellalike ridge (best seenin Stylonu- 
rus myops) | | 
4 The smaller number of body segments (nine or less, seen also in 
S. myops) 
5 The lack of differentiation of the segments 
6 The undeveloped telson 
As differences appear: 
1 The terete or conical abdomen in the young eurypterids in 
contrast with the broadened abdomen of Limulus, and 
2 Large larval eyes in the eurypterids 
We consider both these differential characters as due to purely adap- 
tive changes. The broader abdomen of the larvae of Limulus results from 
the earlier appearance of the broad abdomen of the mature type through 
acceleration, and the adaptive nature of the large larval eyes has been 
fully discussed on page 119. For the reasons here given we find ourselves 
in agreement with those authors who have united the eurypterids and 
limulids under Dana’s subclass Merostomata. 
If the relationship of the eurypterids with the king crabs is so close 
that it places them in one subclass, the eurypterids will have to follow 
the Limulidae in their wanderings in the zoological system. 
The limulids were, as is well known, classed with the crustaceans, 
chiefly on account of their aquatic habit and. branchial respiration, since 
the Arthropod phylum was by common consent divided into two sub- 
phyla, the Branchiata and Tracheata. Opposition arose to this classifi- 
cation through the recognition of the affinities of Limulus with’ the arach- 
nids, first suggested by Strauss-Durkheim, and especially elaborated by 
Van Beneden, Lankester, Kingsley and Laurie, though not without oppo- 
~ sition from such authorities as Packard, Woodward, Thorell and Lindstrom, 
