POLYFLAOOFHOfl 



raucro el 



/ 

 ff. Shell not ^n ally .-IniiL 



g. ( iinllc clothed with large 

 ami small iiit'Tiningled 

 scales, Heterozo 

 gg. Girdle scales regular, uni- 

 form. 



h. 1 slit on each side of 

 median valves 

 i. Girdle scales flat, 

 lachnochiton, p. 86. 

 ii. Girdle scales very 

 convex, 



Lepidozowi, \>. 1 '_'". 

 hh. 2 or more slits on 

 each side, 



i. Girdle scales flat, 

 Eadsiella, p. 139. 

 ii. Girdle scales con- 

 vex, 



Ischnoradsia, p. 144. 



dd. Anterior and side slits corresponding in 

 position with external ribs (Callistoplacinae). 

 e. Surface of valves having strong radial 

 ribs ; girdle densely clothed with im- 

 bricating scales, 



CALLISTOCHITON, p. 260. 

 ee. Surface of valves granulated or peb- 

 bly ; girdle not densely imbricated 

 with scales. 



/. Anterior valve with more than 

 7 slits ; sinus very spongy ; mu- 

 cro posterior, 



NUTTAI.I.INA. J>. -77. 



ff. Anterior valve with ."> slits ; mu- 



cro subcentral, not posterior, 



g. No sutural pore tufts. 



CRASPEDOCHITON, p. 285. 



gg. Sutural pore tufts present, 



A NC.ASIA, p. 286. 



