PLATE XXIII. 
Sponpyius (continued). 
Fras. 
1—5. 8S. Dutempleanus, Orb. (P. 125.) 
1. A. quadratus zone, Whaddon cutting. Dr. Blackmore’s Collection. Left valve 
and umbo of right x 14. 
2. A. quadratus zone, East Harnham, Salisbury. Dr. Blackmore’s Collection. 
Anterior outline showing spines on left valve. 
3. B. mucronata zone, Norwich. Norwich Museum. Right valve. 
4, Chalk of Trimingham. Museum of Practical Geology (Coll. Mr. C. Reid). 
Left valve. 
5. B. mucronata zone, Norwich. Norwich Museum. Part of left valve. 
6—11. SS. spinosus (Sow.). (P. 127.) 
6. T. gracilis zone, Luton. Woodwardian Museum (Coll. Mr. W. Hill). 
a, left valve; b, anterior outline; c, section of ribs of left valve near the mid- 
ventral border x 2. 
7. T. gracilis zone, East Knoyle. Woodwardian Museum (Coll. Mr. Jukes-Browne ). 
8. H. planus zone, Cheveley. Woodwardian Museum. Left valve, with spines 
projecting from the right valve. 
9, Same zone, etc. a, left valve; b, dorsal view; ¢, section of ribs of left valve 
near the mid-ventral border x 2. 
10. Same zone, ete. a, right valve (umbo slightly imperfect) ; 6, section of ribs of 
right valve near the mid-ventral border x 2. 
11. M. cor-testudinarium zone, Chatham. Woodwardian Museum (Coll. Mr. Jukes- 
Browne). a, left valve; b, anterior outline; ¢, ribs of left valve near the mid- 
ventral border x 2. 
