394 Prof. F. M‘Coy on the Classification of 
a difference of superficial sculpturing, I see nothing in it different 
from Eurypterus ; and when we bear in mind that the Idothea of 
Scouler* is avowedly a Hurypterus, I cannot see how Pterygotus 
is to be separated as a genus, at least on any better grounds 
than the above. The tribe Pewcilopoda might be resolved into 
two families: 1st, Limulide, having, besides the head, a second 
shield formed by the anchylosis of all the abdominal segments 
(Limulus) ; 2nd, Eurypteride, having all the abdominal segments 
distinctly separated (Hurypterus, Pterygotus, Bellinurus). The 
first division has not, I believe, been found lower than the oolites, 
the Limuli quoted by several British geologists from the coal- 
measures of Coalbrook Dale, &c. belonging clearly to the second 
division, and should rather be referred to Bellinurus of Konig. 
Pterygotus leptodactylus (M‘Coy). 
Sp. Char. Large pincers having the hand about 5 lines wide, 
sculptured with fine short, irregularly flexuous, elevated lines ; 
the penultimate or immoyeable finger exceedingly slender, 
compressed, about 2 inches 10 lines long, and only 2 lines wide 
at base, gradually tapering to less than a lime towards its ob- 
tuse point, nearly straight, or with a scarcely perceptible in- 
ward curvature ; sides divided into ridges by three or four 
longitudinal furrows, thicker towards the back; last joint 
or moveable finger similar to the immoveable one, but rather 
smaller; inner edges of both fingers destitute of teeth or 
tubercles. 
The pincers, instead of being excessively thick and strong, and 
armed with great teeth on the inner edge as in the Pterygotus 
Anglicus (Ag.), are perfectly unarmed, and so long and slender 
as possibly to indicate a separate subgenus, which might be 
named Leptocheles (NemTos, tenuis, yn», forceps). It strikes 
me (judging from the figures) that the Onchus Murchisoni 
(Ag.) is not an Ichthyodorulite, but the long finger of the 
chelz of this Crustacean,—the size, form and sculpturing agree- 
ing very nearly—while the base presents no trace of the abrupt 
diminution for insertion into the flesh, which would occur in all 
true Onchi. In the same bed with the long chele was found 
a specimen of the terminal or moveable finger, and one’ per- 
fect claw with both fingers in situ of a much shorter form than 
the other; the hand being about 3 lines wide, the penultimate 
immoveable finger about 1 inch long, and rapidly tapering from 
23 lines wide at the base to the obtusely pomted apex ; it is lon- 
gitudinally suleated like the longer one above described ; the last 
jomt or moveable finger is very different, being perfectly flat, trian- 
gular, 7 lines long, 14 line wide at base, and tapering rapidly to 
* See Edinb. Journal of Science, vol. iii. 
