290 SIDNEY v. HARiMEK. 



closure of this species must be remarkably effective. The 

 parallel part of the main sclerite is short, and the cavity 

 therein included is much dilated tr;insversely at its distal 

 end. The proximal ends of the main sclerite are very stout. 

 The A opercula (fig. 40) are large and transversely oblong. 

 There is a distinct basal sclerite and a fine submarginal 

 sclerite in addition to the main strenyftheniny' arch. 



Key to the Species of vStegangporella. 



( a opercula with four teeth on the 



.J main sclerite .... 2 



"I a opercula with two teeth or none 



I . on the main sclerite . . 3 



P A opercula with an enormous sub- 



I basal sclerite . . . .6. S. auriculata. 



I 

 2 <( A opercula with small secondary 



sclerites within the main 



sclerite . . . . .7.S.neozelanica. 



r B opercula with A-shaped main 



I sclerite ..... 



3 <( B opercula with H-shaped main 



j sclerite ; these opercula usually 



I rare ..... 



A opercula with straight or slightly 

 concave distal border, more or 

 less distinctly transversely ob- 

 long*, and with a basal sclerite. 



4 -^ B opercula with stout teeth 

 A opercula with very convex distal 



border, b opercula with minute 

 teeth or none in their proximal 

 half, or with all the teeth small 



