118 NEW YORK STATE MUSEUM 
6 Lhe abdomen lacks distinct differentiation into pre- and postabdomen. 
This condition is made clear by the nearly uniform length of all segments. 
In width there prevails considerable difference, most early growth stages 
appearing to contract more rapidly than the mature individuals, while 
in Hughmiulleria the body is distinctly more slender [pl. 64, fig. 1]. In 
Eurypterus remipes, E. lacustris and especially in 
-E. maria, as well as in Pterygotus buffaloensis there is 
evidence of a relatively broader and shorter preabdomen, although the 
more compact appearance of the preabdomen may be partly due to casual 
contraction after death. 
7 Lhe number of segments ts less in the nepionic stage than in the fol- 
lowing stages. In some nepionic individuals there are not more than six 
segments or half the number normal to the adult [see Stylonurus 
myops, pl. 51, fig. 1]. On account of the smallness of the earliest 
growth stages and the lack of differentiation of the segments we have not 
been able to satisfy ourselves as to whether the preabdomen or the post- 
abdomen is first completed. Thelarvaof Hughmilleria shawan- 
gunk [pl. 64, fig. 1] where a distinct preabdomen with four segments and 
a postabdomen of six segments are noticeable, and some other specimens, 
suggest that the latter was first completed. | 
8 The telson spine may have been less developed than in adults; 
at least such a condition is indicated by several specimens. Unfortunately 
and singularly the telson is nearly always missing in young specimens. In 
the embryo of Limulus there is no tail spine and in the larval stage the 
telson is small. | 
It is now interesting to inquire which of these ontogenetic characters 
are purely larval acquisitions, and which are palingenetic, or of phylo- 
genetic significance as representing the recapitulation of ancestral characters. 
Comparison with the larval stages of Limulus has been of much assistance 
in discerning between these coenogenetic and palingenetic structures. 
The larger size of the carapace we consider as a merely larval char- 
acter, for the following reasons: This larger size is principally due to the 
