262 



Dr. Malcolm Burr on the Opisthomeres 



(i) The basal plate shows traces of a suture in EuhorelUa 



moesta. 

 (ii) The broad base and constricted waist suggest the 



similar form seen in the two distinct corresponding 



plates in Allostethidae. 

 (iii) The rounded lobes at the apex of the basal plates 



seem to correspond with the lobes at the outer 



corner of the metapygidium in the Allostethidae. 



On the other hand, I admit that — 

 (i) The apical plates show transverse lines which may 

 be the suture indicating fusion of metapygidium 

 and telson. 



(ii) In Psalis pulchra and EuhorelUa moesta the apical 

 margin of the apical plate is membranous and 

 seems in the former to have a distinct outline, 

 so that this may be the degenerate membranous 

 telson. 



Fig. 9. — Psalis pulchra, 

 Rehn, $■ 



Fia. 10. — Etiborellia moesta. 

 Gene, ? . 



But on the whole I am inclined to regard the basal 

 plate as the pygidium, the apical one as the metapygidium, 

 and the faint apical membrane as the remains of the 

 telson. 



Zacher states that the suture between telson and 

 metapygidium is sometimes visible, but refers to the apical 

 plate as the supra-anal plate, which name he always uses 

 for the telson. 



