FAMILIES OF LOOP-BEARING BRACHIOPODA 293 



tions and homologies of these parts can best be shown in a 

 series of figures. 



Plate XIV, figures Ci, Di, represent the loop in a young 

 Macandrevia cranium in the so-called platidiform stage, show- 

 ing a complete primary loop and the beginning of a secondary 

 loop in the middle, on top of the septum. A later stage of 

 the same species (Plate XIV, figure GI) has the structure 

 of Terebratalia. The descending lamellae and the median 

 V-shaped plate correspond to the primary loop, while the 

 secondary loop or posteriorly recurved portion has greatly 

 increased in size. A later stage, nearly complete (Plate 

 XXIV, figure 1), shows two points (p) on the descending 

 lamellae, which are remnants of the connecting band in pre- 

 vious stages. The parts homologous with the loop of the 

 first stage and with the loop of Terebratulina are shaded. 

 Greater emphasis is expressed by figures 2, 3, Plate XXIV, 

 where the cirrated brachia and calcareous supports are both 

 represented in the genera Terebratulina and Magellania. It 

 is readily seen that the arm structure is the same in both, but 

 that the calcareous loops which are darkly shaded are very 

 different in form. 



The family Terebratellidae should therefore be reinstated 

 on the evidence here given. The development of Terebra- 

 tella may be reviewed for the leading characteristics of one 

 division of the family. The type is Terebratella chiliensis 

 Broderip, sp. = T. dorsata Gmelin, sp., from the Straits of 

 Magellan. Fischer and CEhlert 8 have described in detail the 

 development of the loop in this form. Their researches also 

 include Magellania venosa Solander, sp., which was found to 

 pass through all the stages of Terebratella dorsata, and after 

 losing the processes connecting the primary lamellae with the 

 septum finally results in adult Magellania. 



MagellaniincB. 



The first stage described by these authors (Plate XIV, 

 figure B) showed only a septum anterior to the middle of the 



