PLATE XXI. 



PRODUCTUS cf. P. SUBACULEATUS, Murchison. (Page 174.) 

 FIG. 



1. Imperfect dorsal valve, with the casts of long spines of the ventral valve. 



Pilton. Porter Collection. 



2. Fragment of the mould of a ventral valve, showing casts of long spines, X f. 



Fremington. Porter Collection. 



3. Worn cast of a valve, showing the scars of spines in transverse rows, X f. 



Fremington. Porter Collection. 



PRODOCTUS CORRUGATUS, M'Coy. (Page 173.) 



4. Oblique view of a worn specimen, with less flexuous ribs than usual. 



Fremington. Porter Collection. 



5. Dorsal valve, most probably of this species, seen from within. Fremington. 



Porter Collection. 



STROPHALOSIA PRODUCTOIDES, Murchison, sp. (Page 175.) 



6. Posterior part of a decayed specimen, which is covered (wherever the surface 



is not totally obliterated) by crowded hair-like spines. Laticosta Cave, 

 Baggy. My Collection. 



7. Dorsal valve, showing hinge-area and hinge-spines ; part of the centre being 



broken away, another specimen is disclosed, which shows the attachment 

 of the spines, X f . 7 a. Portion of the latter specimen, X 8. Poleshill. 

 Porter Collection. 



8. Ventral valve, with very long ribs and hardly any signs of spines, except on 



the hinge. Poleshill. Porter Collection. 



9. Specimen, showing the length of the hinge-spines, X f. Pilton. Porter 



Collection. 



10. Transverse specimen, with short ribs, X f . Poleshill. Porter Collection. 



11. Young specimen, with very few short ribs in the median parts, X 2. 



Poleshill. Porter Collection. 



PRODUCTUS SCABRICULUS, Martin, sp. (Page 170.) 



12. Large elongate dorsal valve, showing the hinge-area. Pilton. Porter 

 Collection. 



