372 NEW YORK STATE MUSEUM 
doubtfully referred to this species a postabdominal segment characterized by 
rather evenly distributed small triangular scales. In form and surface 
sculpture this is identical with the segment of the postabdomen of Eu- 
sarcus scorpionis and quite obviously to be referred to that species. 
The ramus, however, is distinct from that of the chelae of both P. buf- 
faloensis and P. macrophthalmus in the greater relative 
width of its base and its more regular tapering in distal direction; and most 
strikingly by the even rounding of the distal end to form a terminal tooth 
instead of an angular extremity. 
By a strange coincidence, this type which Hall says was the “ fifth 
unequivocal fragment of the genus Pterygotus that came under [his] notice 
seems to represent the rarest of all forms; 
»? 
from any American locality, 
for so far as we know only one other representative of this species has been 
thus far found. This is a ramus about twice as large as Hall’s type. Grote 
and Pitt figured it and referred it to their species P. cummingsi, 
which had been previously described and based upon a coxa. The latter 
probably belongs to P. buffaloensis, while the ramus is not retfer- 
able to that species. These writers cited as distinguishing characters from 
P.cobbi, the difference in size and the fact that the ‘ apex of the joint 
is pointed in P. cummingsi, whilein P. cobbi and P.angli- 
cus it is obtuse.” By the “apex of the joint” the point of the terminal 
tooth is meant. The type of P. cobbi, however, has only obtuse 
teeth and it is obvious that this is entirely due to weathering. To the 
same cause and the poor preservation of the type in general may be 
also attributed the absence of the smaller intercalated teeth in both 
specimens. : 
The question suggests itself whether old age could not have produced 
in P. buffaloensis or P. macrophthalmus a free ramus 
like that upon which this species is based; or whether it might not be 
indicative of a slight variation only. The first suggestion is refuted by 
the presence in our collection of free rami of buffaloensis of similar 
size, with typical angular points of the jaws; and perhaps still more by 
