PLATE XIII. 
Page. 
Fig. 1. Spii'ifer Strzeleckii, L. G. de Koninck — Internal cast, seen from the dorsal side 183 
Fig. Iff. The same, seen from the ventral side ... ... ... ... ... ... 183 
Fig. 2. Spirifer ClarJcei, L. G. de Koninck — Specimen, seen from the dorsal side ... 184 
Fig. 2ff. The same, seen from the ventral side ... ... ... ... ... ... 184 
Fig. 3. Spirifer convolui us, ^.V\n\\\p9, — Internal cast, seen from the ventral side ... 187 
Fig. 3ff. The same, from the hinge face ... ... ... ... ... ... ... 187 
Fig. 3J. Another internal cast, seen from the dorsal side ... ... ... ... ... 187 
Fig. 3c. The same, seen from the ventral side ... ... ... ... ... ... 187 
Fig. 4. Spirifer vespertilio, G. Sowerby — Internal cast, seen from the dorsal side ... 189 
Fig. 4ff. The same, seen from the ventral side ... ... ... ... ... ... 189 
Fig. 4S. Another internal cast, seen from the dorsal side ... ... ... ... ... 189 
Fig. 4c. The same, seen from the ventral side ... ... ... ... ... ... 189 
