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 Eurypterus, I cannot see how Pterygotus 

 is to be separated as a genus, at least on any better grounds 

 than the above. The tribe Pcecilopoda might be resolved into 

 two families : 1st, Limulidce, having, besides the head, a second 

 shield formed by the anchylosis of all the abdominal segments 

 (Limulus) ; 2nd, Eurypteridce, having all the abdominal segments 

 distinctly separated (Eurypterus, 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 immoveable finger exceedingly slender, 

 compressed, about 2 inches 10 lines long, and only 2 lines wide 

 at base, gradually tapering to less than a line 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 (Xeirrbs, tenuis, XV^V} forceps). It strikes 

 me (judging from the figures) that the Onchus Murchisoni 

 (Ag.) is not an Ichthyodorulite, but the long finger of the 

 chelae 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 chelse 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 

 2| Jines wide at the base to the obtusely pointed apex ; it is lon- 

 gitudinally sulcated like the longer one above described ; the last 

 joint or moveable finger is very different, being perfectly flat, trian- 

 gular, 7 lines long, 1^ line wide at base, and tapering rapidly to 



* See Edinb. Journal of Science, vol. iii. 



