THE EURYPTERIDA OF NEW YORK 429 
A comparison of the structure here described with that of Pterygotus 
shows that the epistomas of both genera agree in general form. That of 
Hughmilleria is, however, the longer and more slender, an adaptation to 
the more elongate form of the head shield in that genus, and there are in 
Pterygotus no antelateral shields separated by sutures from the marginal 
shield. 
The epistoma exists, so far as we now know, in no other genera than 
Hughmilleria and Pterygotus; that is, in the two genera which are charac- 
terized by a very strong development of the chelicerae, and this fact indi- 
cates that the plate itself has resulted from strains originating from these 
strong and active arms. 
NOTE ON PTERYGOTUS COBBI var. JUVENIS nov. 
See text figures 119-21 
In the description of P. cobbi, in the body of this memoir, we 
had only two free rami of the pincers at our disposal, all that was known 
of the species. A large collection of eurypterid material since obtained 
by Mr Hartnagel in Herkimer county, contains two small specimens of 
Pterygotus on the same slab, one of which possesses the characteristic 
pincer of P. cobbi with some slight differences, of such nature as to 
be quite probably ascribable to an earlier growth stage of the species. 
We therefore refer to these specimens as P, cobbi var. juvenis. 
These two specimens differ in a number of characters from both the 
common P. buffaloensis of the Bertie waterlime at Buffalo and 
the P. macrophthalmus of Herkimer county. The most im- 
portant of these differences rests in the pincers which 
tees) | are rounded in front as in P. cobbi and the free 
ramus of which shows the denticles of the type of 
Fig. 119 Pterygotus - : ee ; : 
cop Pincers xs "'* that species but is stouter and distinctly higher in the 
middle. The carapace is more evenly rounded anteriorly than in the other 
two species here cited and especially longer (length to width as 4 :5); the 
compound eyes are relatively larger while the abdomen appears slightly 
broader and stouter (the preabdomen is 26 mm long and 19 mm wide); 
