EXPLANATION OF PLATE XLII. 



All of the figures on this plate, except 21 and 22, are copied from Ulrich and 



are X 20. 



Figs. 1-4. Treposella lyoni (Ulrich). 

 1. Side view of a right valve. 

 2, 3. Dorsal and posterior views of the same specimen. 



4. A left valve showing the subcentral ventral pouch. 

 5-7. Hollina kolmodini (Jones). 



5. A right valve showing the similarity of the ridges to Drepanella. 



6. Interior of a right valve. 



7. Dorsal edge view of same. 

 8,9. Hollina insolens (Ulrich). 



8. Exterior of a left valve. 



9. Interior of another left valve. 

 10-12. Hollina cavimarginata (Ulrich). 



10,11. Lateral and posterior views of a left valve. 



12. View of interior of another left valve. 



13. Hollina spiculosa (Ulrich). 



Side view of a nearly perfect right valve. 



14. Hollina annata (Ulrich). 



A right valve showing the usual characters. 



15. Hollina tricollina (Ulrich). 

 Lateral view of a left valve. 



16,17. Hollina granifrra (Ulrich). 



Lateral and posterior views of a right valve. 



18. Hollina radiata (Jones and Kirkby). 



Right valve of an American example, apparently agreeing in all es- 

 sential respects with the English types of the species. 

 19,20. Hollina radiata cestriensis (Ulrich). 



19. Side view of a left valve, X 28. 



20. Posterior view of same example. 



21,22. Beyrichiat tuberculospinosa Jones and Kirkby. 



Side views of two examples of this doubtfully placed Carboniferous 

 species, which may be a Hollina, X 25. (After Jones and Kirkby.) 

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