BRACHIOPODA. 



59 



probably owing to the attachment of the shell when young 

 (= Streptorhy?ichus, King). In Strophomena, Safin ( =Leptcena, 

 Dalm., fig. 13, 3), there is a minute byssal foramen when young, 

 of which no trace exists in the adult ; and the deltoid notch is 

 also closed, except the space required to receive the divided 

 cardinal process of the dorsal valve. The oral processes 



Fig. 13. 

 Brachiopoda. 



1 . Orthis hysterita, L. (cast) ; Devonian, Rhine. 



2. Davidsonia Verneuili, Bouch. ; Devonian, Eifel. 



3. Strophomena rhomboidalis, Wahl. ; U. Silurian, Dudley. 



4. Producta semireticulata, Martin ; Carboniferous, Derbyshire. 



5. Chonetes striatella, Dalm. ; U. Ludlow rocJc, Herefordshire. 



6. Calceola sandalina, Lam. ; Devonian, Eifel. 



7. Obolus Apollinis, Eichw. ; L. Silurian, Northern Europe. 



8. Siphonotreta unguiculata, Echw. ; U. Silurian, Britain. 



appear to be shifted to the centre of the valve. The shell, 

 when young, is plano-convex, but when it has attained a certain 

 size the valves are bent over to one side or the other, and more 

 or less suddenly. The pallial impressions are the same as in 

 Orthis. 



The genus Davidsonia (fig. 13, 2), peculiar to the Devonian 

 limestones, resembles an Orthis attached, like Thecidium, by 

 the ventral valve to corals, and sometimes taking the mark- 



