6 



PEOCEEDINGS OF THE NATIOISrAL MUSEUM 



VOL. 78 



backwards. When compressed the outer surface of the appendage 

 would then cover the inner edge as is actually found in the speci- 

 mens. In no case can the insertion of the setae on the inner edge 

 of the appendage be unequivocallj- made out, but it is probable that 

 there was no very unequal development of certain endites for the 

 setae are very evenly developed throughout the whole length of the 

 appendage. 



app.H 



Figure 2.— Opabinia regalis Walcott. a, Posterior 

 END OF coTYPB (U.S.N.M. 57683) ; app. U, left append- 

 age OF FOURTEB.NTH TRUNK SOMITE ; app. I'l, RIGHT AP- 

 PENDAGE OP FIFTEENTH TRUNK SOMITE (X 5). 6, LEFT 

 APPENDAGE OF SEVENTH TRUNK SOMITE OF COTYPB (U.S. 



N.M. 57684) (X 5) 



The last pair of appendages, on the fifteenth segment, was clearly 

 not directed ventrally in life but more laterally than those at the 

 anterior end of the body. In specimen 56783 it consists of a flat 

 platelike structure, the edges of which are imperfectly preserved. 

 (Fig. 2.) The plate lies at a lower level than the rest of the 



