FAMILIES OF LOOP-BEARING BRACHIOPODA 301 



form stage of Macandrevia, Dallina, Laqueus, and the adult 

 structure of MilJilfeldtia sanguinea. After this, the union of 

 the primary and secondary loops and their removal from the 

 septum to which they remain attached only by connecting 

 processes form a structure like that in Laqueus (figures G4, 

 Gs), and the resorption of the connecting bands from the 

 ascending branches of the loop completes the terebrataliform 

 stage of Macandrevia and Dallina^ as shown in Plate XIV, 

 figures Gi, G2. Terehratalia is the present fixed genus of 

 this type of structure (figure G3), and Trigonosemus (figure 

 G5), is a Cretaceous representative. Finally, by the resorp- 

 tion of the bands of the terebrataliform stage, the structure 

 of the highest genera, Macandrevia and Dallina, is reached 

 (figures H1-H5). 



The first stage after the cistelliform in the Magellaniinae, 

 the austral branch of the Terebratellidse, is represented for 

 Terehratella dorsata, in Plate XIV, figui*e Ca. Kraussina 

 (figures C6, Cc) has a simple fork or V-shaped process on the 

 septum, which apparently represents an incomplete secondary 

 loop. The relations of Bouchardia (figure Qd) to this 

 bouchardiform stage of Terebratella are more evident. After 

 this stage the beginnings of the primary loop, or descending 

 branches, appear as two projections on each side of the 

 septum (figure Da'). Megerlina (figure D6) shows this ad- 

 vance over Kraussina. 



The completion of the descending branches in the next, or 

 magadiform, stage is represented for Terebratella dorsata, in 

 Plate XIV, figure Ea ; T. cruenta, figure Ec ; T. rubicunda, 

 figure Ec? ; Neothyris lentieularis, figure E5 ; Magasella Cum- 

 ingi, figure E/. The Cretaceous equivalent, Magas, is shown 

 in figure Eg. In all these forms the septum projects above 

 the descending lamellse nearly to the ventral valve. 



T. Buckmani Moore, figure Fe). A strict interpretation of that genus based upon 

 T. dorsata, the type, excludes these species, whicli agree with the definition of 

 Ismcnia in that the ascending and descending branches are attached directly to 

 the septum. They may be, however, stages of growth of higher forms. 



