CRUSTACEA. 141 



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 (XeTrro?, 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 

 chelse 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| lines 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, l^ line wide at base, and tapering rapidly to 

 a point, the inner edge being straight and simple, the outer edge 

 slightly convex. The hands of both kinds of chelse are similarly 

 sculptured with short, fine, sharp, irregularly curved, longitu- 

 dinal plicae, proving their identity, and that thus, like the recent 

 Poecilopoda, more than one pair of feet were didactyle. 



In the fine olive schists (of the age of the Upper Ludlow 

 rock) of Leintwardine. 



(Col. University of Cambridge.) 



(New genera and species of Trilohites *.) 



Chasmops (M'Coy), n. g. 



Etym. x^a-fjLa, hiatus, and ooylr, oculus. 



Gen. Char. Cephalic shield ?,\\}o^tTmc\rcvldiX, lateral angles produced 

 backwards in triangular spines ; glabella 

 large, clavate, frontal portion very wide, 

 transversely oval, only two distinct pairs 

 of lateral segmental lobes, the anterior 

 pair very large triangular, posterior pair 

 small, middle pair obsolete or reduced to 

 a minute tubercle on each side; neck- 

 segment strong : cheeks small triangu- Cephalic shield of 

 lar : eyes small, rounded, ^^ hiant," corre- asmops. 



* See Annals of Nat. Hist, for December 1849 for some obsei'vations on 

 the classification of Trilohites and the structure of their pleurae, homologies 

 of the cephalic shield, &c. 



