376 NEW YORK STATE MUSEUM 
The swimming leg [pl. 81, fig. 10] agrees with the corresponding organ 
of its allies in its smaller elongate paddle and long seventh segment. 
Metastomas and telsons, referable to Pterygotus, have also been 
observed in the Otisville beds. The latter are of bilobed form and indicate 
Huxley & Salter’s genus Erettopterus. The half of one telson, obviously 
too short, through anteroposterior compression shows a fringe of very 
minute, acute points such as have, to our knowledge, not been observed 
before on the telson of a Pterygotus. Smaller specimens (as that reproduced 
in plate 82, figure 12) are better preserved and consist of elongate bilobate 
bodies with a central, posteriorly tapering, raised axis. The lobes are broad 
and well-rounded. | 
While the carapace of this species strikingly resembles that of 
P.(Erettopterus) bilobus Huxley & Salter [see -especially 
Woodward, 1869, pl. ro, fig. 3] in its subcircular outline and larger eyes, 
the telsons from Otisville are much shorter and less bilobed and can be only 
compared to those of P. (Erettopterus) banksii [Huxley & 
Salter, Monogr. pl. 12, fig. 23, 36, 37]. Both carapaces and telsons thus 
show closest relationship to species of the subdivision Erettopterus, a fact 
that argues for the union of the carapace and telsons. 
Ontogeny. By far the most interesting part of this small series of 
specimens are the four immature individuals [pl. 82, fig. 1-4] which give 
us the first information on the ontogeny of a Pterygotus. Of these four 
two are clearly in a larval condition and represent the nepionic stage, 
while the others have certain characters in common which, together with their 
size, support the view that they are still immature and belong to the 
type intermediate between the nepionic and ephebic conditions. 
The two nepionic specimens are characterized above all by the rela- 
tively great size of the carapace, the small size of the abdomen and small 
number of segments. The carapace occupied nearly one third the length 
of the whole body while in the mature P. macrophthalmus, 
the only species of which we have whole individuals, it reached only about 
one eighth the length of the body. The fourth figure indicates how far in 
