THE EURYPTERIDA OF NEW YORK 117 
size of the compound eyes is a prominent feature of all very young stages 
here investigated and seems to be a general ontogenetic character. In 
one species, Pterygotus globiceps, the eyes are not notably 
larger than in the ephebic individual, but in this case they are very large 
at maturity and obviously a retained larval character. InEurypterus 
maria, Pterygotus macrophthalmus and Hughmil- 
leria shawangunk the difference in size is especially notable. In 
Stylonurus myops the visual area exhibits little difference in rel- 
ative size, but the ocular nodes are so extended that they occupy nearly 
’ the entire dorsal side of the carapace within the flat border. 
3 The compound eyes are nearer to the margin; either the anterior 
margin (Eurypterus), or the lateral (Stylonurus myops). In 
Pterygotus and Hughmilleria they are already marginal in the nepionic 
stage and remain so to the ephebic stage. 
4. The ocellar mound or tumescence exhibits a distinct tendency to both 
larger size and greater prominence in the earlier growth stages than in the adult, 
This ontogenetic feature has been especially noted in Eurypterus 
remipes, E. maria, Pterygotus macrophthalmus 
and Hughmilleria shawangunk. There is also evidence that 
the ocelli themselves are relatively larger. 
5 the swimming legs are, as a rule, larger. This has been noted in 
Eurypterus remipes, E. maria and Pterygotus buf- 
faloensis. The great majority of all larval individuals have lost the 
appendages. The specimen reproduced on plate 21, figure 5, shows the 
relative great size and width of the swimming legs in E. maria. 
Of much interest in this connection is a larval specimen of St ylo- 
nurus myops exhibiting the metastoma in fine preservation [pl. 51, 
fig.6]. The latter is of immense size, almost equaling the carapace in length. 
As the metastoma is correlated in size to the coxae of the swimming legs 
it would follow that the latter must have been enormously developed in 
this species and the larvae highly agile. The probable activity of the 
larvae is further suggested by the enormously bulging eyes. 
