PLATE XXXIII. 



PeOTEN {roufhiin'd). 

 Fedeii {Chhuni/s) crcfo^us, Defr. Upper Chalk. (P. 174.) 



Figs. 



1. A. ([iKiilnifiis zone, East Haniham. Dr. Blackmore's Collection, a, right 



valve X 1^ ; Ji, part at antero-ventral edge X 4 ; r, antero-ventral part 

 of left valve of the same specimen X 4. 



2. Same horizon, etc. a, left valve ; h, part just behind the mid-ventral edge 



X 3. 



3. Same horizon, etc. a, left valve x 11 ; A, part at postero-ventral margin 



X 4. Fine concentric ridges cover almost the entire shell, but are not 

 shown in the figure. Near the nmbo the radial ribs are spiny. 



4. M. cor-dngtiriuiiih zone, Porton. Dr. Blackmore's C^ollection. r?, left valve; 



h, part just behind the mid-ventral mai'gin x 3. 



5. Marsujntes zone, Witherington. Dr. Blackmore's Collection. Left valve. 



6. M. cor-<fiif/innum zone, Gravesend. Mr. G. E. Dibley's Collection, a, right 



valve, with interior of anterior hff ear ; h, part of mid-ventral third 

 X 4. 



7. Upper Chalk, Bromley. Wiltshire Collection. Right valve of specimen with 



coarse ribs, a, antero-ventral part; />, portion of same part X 3. 



8. Same horizon, etc. Part of mid-ventral third of left valve X 6. 



9. 7?. ruiicroiiiifii zone, Norwich. Norwich Museum, No. 205G. Part of left valve 



near the middle of the ventral edge X 4. 



10. A. quadratus zone. East Harnham. Dr. Blackmore's Collection. Part at the 



mid- ventral edge X 4. 



11. Upper Chalk, Charlton. Wiltshire Collection. Right valve of a specimen 



with the scaly spines large and well-preserved. Part near the ventral 

 edge X (). 



12. LTpper Chalk, Trimingham. IMr. R. M. Brydone's Collection. Right valve. 



Form with numerous slender ril)s. Portion at the dorsal third X G. 



