PLATE X. 
Page. 
Fig. 1. Productus magnus, F. B. Meek and A. H. Wortheu — Specimen, seen from the 
ventral side ... ... ... ... ... ... ... ... ... 142 
Fig. \a. The same, seen from the opposide side 142 
Fig. 2. Prodtictus gimctatus ,'^ — Internal impression of the dorsal valve ... 14S 
Fig. 3. Producius fragilis, ^ .'D.V^&wa — Internal cast of the ventral valve ... ... 155 
Fig. 3a. Internal cast of the dorsal valve ... ... ... ... ... ... ... 155 
Fig. 4. Productus brachgtlicsrus, Gr. Sowerby — Specimen, seen from the ventral side ... 153 
Fig. 4a. Internal cast of the ventral valve ... ... ... ... ... ... ... 153 
Fig. 5. P/’odac/as C'/ar^-ei, E.. Etheridge — Interior of the dorsal valve... ... ... 153 
Fig. G. Chonetes i^api^ionacea, Z . Vh.\\\i \>^ — Ventral valve of a young individual ... 158 
Fig. 7. Ghoneies Laguessiana, L. G. de Kiouiuck — Ventral valve, view from above ... IGO 
Fig. 8. Ortholetes crenistria, J. Phillips — Internal impression of the ventral valve ... 1G4 
Fig. 8a. Fragment of the same, enlarged ... ... ... ... ... ... ... 1G4 
Fig. 9. Orthis resupinata, W. Martin — Ventral valve, seen from the front ... ... IGG 
Fig. 9a. Internal cast of the ventral valve ... ... ... ... ... ... ... IGG 
Fig. 9S. ,, „ dorsal valve ... ... ... ... ... ... ... IGG 
Fig. 10. Orthis Ilictielini^ C. 'LcxeiWe — Ventral valve of a young individual ... ... IGS 
Fig. 10a. Internal cast of the dorsal valve of an adult ... ... ... ... ... 1G8 
Fig. 11. Spirifer Darwinii, ^ . 'Movns , — Young individual, seen from the dorsal side ... 179 
Fig. 11a. The same, seen from the ventral side ... ... ... ... ... ... 179 
Fig. Hi. Spirifer duodecimcostatus, F. MeCpy — internal cast, seen from the ventral 
side. [This last figure is, in the explanation of the plate in the original, 
marked 12 and Hi on the plate.] ... ... ... ... ... ... 182 
