FAMILIES OF LOOP-BEARING BRACHIOPODA 299 



ing bands from the septum, result in Laqueus (figures G4, 

 Gs), which has connecting bands from the ascending to the 

 descending lamellae and from the latter to the septum.* 



The absorption of the connecting bands from the ascend- 

 ing branches completes the Terebratalia stage (Plate XIV, 

 figures Gi, Ga), in Macandrevia and Dallina, and is the adult 

 condition in Terebratalia transversa^ T. obsoleta, T. frontalis, 

 and T. coreanica (figure G3).f 



Finally, the resorption of the connecting bands from the 

 descending branches produces the Dallina structure, and the 

 further resorption of the septum terminates the series in 

 Macandrevia (Plate XIV, figure Hi). 



Comparisons and Homologies. 



Thus the genera of the Terebratellidse begin their larval 

 development in a form like Gwynia, having no calcified 

 brachial supports, and with a simple circle of centripetally 

 directed tentacles. Then by the growth of a septum in the 

 middle of the dorsal valve, a cistelliform stage is reached. 

 From this point divergence begins, and there is one series 

 of transformations resulting in Macandrevia, and another 

 terminating in Magellania, the mature loops in both groups 

 being practically alike. Macandrevia and Dallina are mor- 

 phically equivalent to MageUania, and Terebratalia is also in 

 exact parallelism with Terebratella. 



A more graphic presentation of the development and rela- 

 tions of the genera is shown on Plate XIV, in which the stages 

 of growth of Magellania and Macandrevia are represented 

 on two ontogenetic lines. Outside are placed other species 

 and genera, with their known stages of growth so arranged 



* The name Megerlina Jeffrey si was given to a stage of Laqueus californica 

 from its having a structure like Megerlina (= Muhlfeldtid) truncata, thus indi- 

 cating clearly the close relationship of these genera. 



t T. spitzbergensis and T. Marice, from the unfinished appearance of their 

 brachial supports, possibly will be found to belong to a higher member of the 

 series ; for example, Dallina. 



