THE EURYPTERIDA OF NEW YORK 383 
Remarks. The outline of the carapaces is quite variable, at times 
being nearly quadrilateral [pl. 86, fig. 3], at others almost semicircular. 
Much of this diversity of form is obviously due to the compression and 
wrinkling of the rather flaccid carapaces in different directions, but in the 
best preserved specimens there is still an element of difference left after 
allowing for all the secondary influences that suggest the presence of more 
than the two species of Pterygotus here described and a distinction between 
the round and the squarish carapaces. This suspicion is strengthened by 
the evidence from the patches of integument showing patterns of ornamen- 
tation which also indicate a greater number of species of Pterygotus. We 
have selected the squarish specimens as typical of P. prolificus. 
Disjecta membra of Pterygotus from the Frankfort shale 
Besides the carapaces here used for specific diagnosis, many other 
fragments are referable to Pterygotus. The most characteristic of these 
may be briefly noted. 
Plate 86, figure 19 represents a fragment of the arm of a pincer. 
_ The distal end of a swimming leg, which in the form of the seventh 
and eighth segments resembles the leg of a Pterygotus more than that 
of any other genus, is reproduced in plate 86, figure 16. In the same group 
belongs plate 86, figure 20. There occur entire large swimmung legs which 
probably belong to O. prolificus. Another very characteristic 
‘group of fragments are the female opercular appendages [pl. 87, fig. 
1-3]. They resemble those of the giant P. anglicus and from their 
dimensions may belong to P. prolificus. Stil another form of a 
large appendage corresponding to a type observed at Otisville, is seen in 
plate 87, figure 4. The most remarkable of the opercular appendages is 
one [pl. 86, fig. 11] which beautifully retains the characteristic broad 
overlapping crescent-shaped scales of the Pterygotus-Slimonia group. This 
resembles the male opercular appendage of Slimonia. 
The metastoma reproduced in plate 86, figure 17, resembles in the 
anterior half, which alone is preserved, so much the metastomas of several 
species of Pterygotus and also corresponds in its large size so perfectly 
to the partsof P. prolificus that there is little doubt of its belong- 
ing with the large carapaces of that species. 
