FAMILIES OF LOOP-BEARING BRACHIOPODA 301 



form stage of JIacandrevia, BalUna, Laqueus, and the adult 

 structure of Milhlfeldtia sani/uinea. After this, the union of 

 the primar}^ 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 Gi, 

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

 ascending branches of the loop completes the terebrataliform 

 stage of 3Iacandrevia and Ballina, as shown in Plate XIV, 

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

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

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

 tion of the bands of the terebrataliform stage, the structure 

 of the highest genera, 3Iacandrevia and Dallina, is reached 

 (figures Hi-Hs). 



The first stage after the cistelliform in the Magellaniinte, 

 the austral branch of the Terebratellidse, is represented for 

 Terebratella dorsata, in Plate XIY, figure Ca. Eraussina 

 (figures C5, Co) has a simple fork or V-shaped process on the 

 septum, which apparently represents an incomplete secondary 

 loop. The relations of Bouchardia (figure Cd") 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 DJ) 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 Fid ; Neothyris lenticularis, figure E5 / Magasella Oum- 

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

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

 the descending lamellae 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, which agree with the definition of 

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

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



