384 MR. E. S. COBBOLD ON THE [vol. lxxvi, 



Orusia lenticularis Wahlenberg, X 4, see p. 354; horizon Ca. 



Fig. 25. Dorsal valve, internal cast, with posterior view, showing casts of 

 convergent crural plates [2509]. 



26. Ventral valve, internal cast, showing casts of divergent dental 



plates [2507]. 



27. Ventral valve, exterior, with lateral outline ; and dorsal valve, internal 



cast, showing casts of parallel crural plates [2516]. 



Obolus sp. indet. b, X 6, see p. 340 ; horizon Bb L ,. 

 Fig. 28. Ventral valve, internal cast [1621]. 



Obolus sp. indet. a, X 6, see p. 340 ; horizon Ba ,. 

 Fig. 29. Dorsal (?) valve, external cast [1604]. 



Acrotreta sp. indet. b, see p. 348 ; horizon Ba,. 

 Fig. 30. Ventral valve, crushed exterior [1606]. 



Plate XXIV. 

 Lapworthella nigra, gen. et sp. nov., X 10, see p. 360 ; horizon Ad. 



Fig. 1. Exterior of attenuate example, slightly damaged [BE. 1221], 



2. Internal cast, with shell in section [266], 



3. Surface of inner shell, showing (where broken away) a portion of the 



internal cast [BE 1221]. 



4. Exterior of wide example, somewhat worn [BE 1221]. 



5. Interior of outer covering, with portion of inner shell adhering ^267]. 



6. Wide individual, detached from the matrix and somewhat abraded : 



a, summit; b, lateral view [270]. 



Helenia cancellata, sp. nov., X 4, see p. 363 ; horizons Ac 2 to Ad. 



Fig. 7 a. Type- specimen, external impression, with closed end preserved [246], 

 Ac 2. 

 7 b. Same individual, showing marginal groove [245], Ac 2 . 

 8. Another closed end [243], Ac 2 . 

 9«. Another specimen X 4 [246], Ac.,. 

 9 b. The same X 10, with section. 

 10. Diagram, showing character of sculpture. 



Hyolithus (Orthotheca) bayonet, var. striatus nov., X 4, see p. 357; 

 horizon Ac 4 . 



Fig. 11. One of the ventral faces, with section [231]. 



Hyolithus (Orthotheca) bayonet Matthew, X 4, see p. 357; horizon Ac-. 



Fig. 12. Dorsal face [2567]. 



13. Dorsal apertural margin, external cast [2572]. 



14. Dorsal face, fragment, with section [2568]. 



15. One of the ventral faces [2576]. 



16. Section, more in accordance with Dr. Matthew's description than 



fig. 14 [1672]. 



Hyolithus (Orthotheca) co'mpressus, sp. nov., X 4, see p. 357 ; horizon Ac 2 . 



Fig. 17. Type-specimen; a, part of an external cast, with outline of curvature 

 [225] ; b, exterior, with section [226]. 



