PLATE X. 



Fig. 1. — Parallelodon reticulatus. A right valve, having the test very finely preserved. From 

 the Carboniferous Limestone of Castleton. My Collection. (Page 142.) 



Figs. 2, 3. — Parallelodon reticulatus. The casts of a right and left valve, showing the adductor 

 muscle-scars and pallial line, Fig. 2, having a small portion of test preserved. Same locality. My 

 Collection. (Page 142.) 



Fig. 4. — Parallelodon reticulatus. A beautifully marked example with finer radiating lines than 

 the Castleton specimens, from the Carboniferous Limestone of Settle. In the Burrow Collection of 

 the Woodwardian Museum, Cambridge. (Page 142.) 



Fig. 5. — Parallelodon cancellatus. A testiferous example of a left valve, beautifully preserved, 

 from the Carboniferous Limestone of Settle. My Collection. (Page 144.) 



Fig. 6. — Parallelodon cancellatus. The cast of a right valve, showing the posterior teeth, from 

 the Carboniferous Limestone of Park Hill. My Collection. (Page 144.) 



Fig. 7. — Parallelodon cancellatus. A left valve, the type specimen of Sowerby's, and probably 

 also of Martin's, Area cancellata, from the Carboniferous Limestone of Derbyshire. In the Sowerby 

 Collection, British Museum (Natural History), South Kensington. (Page 144.) 



Fig. 8. — Parallelodon cancellatus. The cast of a very large example, left valve, from the 

 Carboniferous Limestone of Park Hill. In the Collection of the Geological Survey, Jermyn Street. 

 (Page 144.) 



Fig. 9. — Parallelodon cancellatus. The cast of the right valve, showing the impressions of the 

 posterior teeth of the hinge. Fig. 9 a, an enlarged view. Same locality and Collection. (Page 144.) 



Fig. 10. — Parallelodon Lacordairianus. A fine example of the left valve, from the Carboniferous 

 Limestone of Castleton. My Collection. (Page 147.) 



Figs. 11, 12, and 15. — Parallelodon Walciodorensis. A. series of right valves, from the Carboni- 

 ferous Limestone of Settle. In the Burrow Collection of the "Woodwardian Museum, Cambridge. 

 (Page 149.) 



Fig. 13. — Parallelodon Walciodorensis. A full-grown example of the right valve, from the 

 Carboniferous Limestone of Castleton. My Collection. (Page 149.) 



Fig. 13 a. — Parallelodon Walciodorensis. The same shell, showing a small portion of the anterior 

 part of the hinge of oblique teeth exposed. (Page 149.) 



Fig. 14. — Parallelodon Walciodorensis. The cast of a right valve, showing the adductor muscle- 

 scars and the pallial line. Fig. 15, showing shell surface. Same locality. My Collection. 

 (Page 149.) 



Fig. 16. — Parallelodon corrugatus. A left valve, with a portion of the test preserved, showing 

 the peculiar and characteristic ornament, and also exposing the posterior adductor scar and the 

 pallial line. From the Carboniferous Limestone of Settle. In the Burrow Collection of the "Wood- 

 wardian Museum, Cambridge. (Page 140.) 



Fig. 17. — Parallelodon corrugatus. A rolled specimen of the left valve, showing the broad 

 ligamental area and thickened hinge-plate, but no details are preserved. Same locality and Collection. 

 Fig. 17 a, another view of the wide area of the same specimen. (Page 140.) 



Fig. 18. — Parallelodon corrugatus. The portion of a specimen having the test preserved 

 figured to show the transversely corrugated ornament. Same locality and Collection. (Page 140.) 



Fig. 19. — Parallelodon corrugatus. A testiferous example of the left valve, from the Carboni- 

 ferous Limestone of Castleton. My Collection. (Page 140.) 



