THE EURYPTERIDA OF NEW YORK IIg. 
lack of development of the abdomen in the earlier stages and corresponds 
to a like antecedence in development of the cephalothorax in Limulus 
especially manifest in the embryological stages. From geological evidence 
and theoretical reasons, just the reverse is to be postulated in the phylogeny 
of the eurypterids, 1.e. an earlier weaker development of the cephalothorax. 
The greater size of the carapace in such trilobites as Harpes is considered 
as a larval character retained to maturity, but this is no evidence 
of the primitive character of the genus. Likewise eurypterids with large 
carapaces, as certain species of Eurypterus, are not at all to be considered 
as primitive. The philosophy and phylogeny of the arthropods agree in 
postulating a gradual growth and consolidation of a greater number of 
segments into the cephalothorax. The smaller cephalothorax is therefore 
to be considered as the more primitive and the evidence from such euryp- 
terids as the Cambric Strabops and the simpler species of Eurypterus, is 
not contradictory to this conclusion. Altogether the remarkably small 
size of the cephalothorax of the eurypterids in comparison with the abdo- 
men is to be considered as one of their most striking primitive characters. 
The larger size of the larval eyes is regarded by us as a larval char- 
acter without phylogenetic significance. It finds its striking analogy in 
the megalops stage of the crustaceans, well shown in the common crab 
Callinectes [see text fig. 23]. In this stage the eyes are not only of excessive 
size, but also situated at the ends of very 
movable stalks. In the larvae of the euryp- \ 
terids the lateral eyes were not only of large \\ 
size but also borne on very high and large 2 prenereied 
ocular nodes (particularly well shown in Sen EET 4 SN 
_sStylonurus myops), giving them a Cn RSE ea , 2) 
sags 
like prominence. None of these features is 
observable in either the larvae of Limulus NN Y a 
or of the scorpion and we have probably to \ j 
regard them as larval features peculiar to the Figure 23  Megalops-stage of the 
. common crab (Callinectes 
young of the eurypterids. hastatus). (From Brooks) 
