THE EURYPTERIDA OF NEW YORK 379 
Pterygotus (Erettopterus) grandis (Pohlman) emend. 
Plate 31 
Ceratiocaris grandis Pohlman. Buffalo Soc. Nat. Hist. Bul. 1883. 4: 109, 
fig. 5 
The waterlime at Buffalo has furnished the broad symmetrical remains 
of a creature described by Pohlman as the carapace of a gigantic Ceratio- 
caris on the assumption that the two semicircular valves of this supposed 
phyllocarid had been spread out on both sides of the dorsal line. This view 
is Clearly erroneous and the fossil is the telson of a Pterygotus. According 
to Pohlman it was found in the same bed which yielded the Pterygotus. 
The specimen represents the section with bilobed telson (Erettopterus). 
Pterygotus banksi1i, a British Lud- 
low form, possessed a similar telson [Huxley 
& Salter, Monogr. pl. 12, fig. 45] although it is 
considerably surpassed in transverse develop- 
ment by this American species. 
As a telson this fossil is characterized by 
. . . oe Figure 80 Original figure of Cer- 
the anterior transverse hinge line where it is “ 4.004 Tae grandis Pohl- 
connected with the preceding segment, the ™” 
smooth antelateral edge and the scalloped postlateral edge. The anterior 
half is provided with a median ridge while the posterior part is divided by 
a median cleft. It is probably the character of this median line which 
led to the reference of the fossil to Ceratiocaris. 
The form of the telson is transversely elliptic with rather acute ends. 
_Its major diameter, 24 cm, is to the minor as 12:7. The anterior hinge 
line is but 69 mm long, thus indicating the broad flaring character of 
the telson in comparison to the postabdomen. The scallops are broad 
and shallow; at the termination of the median line is’a deeper and broader 
emargination. The sides of the median cleft are curved outward and 
overlap considerably. The surface is very finely granulated. 
This telson must have been the effective propelling organ of a gigantic 
merostome, which was undoubtedly 5 feet or more in length. In view of 
