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than probable, therefore, that the ancestors of these species which possessed 

 Magaselliform and Terebratelliform loops also had Bouchardiform shape 



Fig. 4. — Species of Boiichardia. a-d. South American (after Ihering). a. B. zitteli 

 . Ihering (twice natural size), b. B. patagonica Ihering (twice natural size), Pata- 

 gonian formation, c. B. zitteli Ihering, holotype (twice natural size), Patagonian 

 pj formation, d. B. transplatina Ihering (very slightly enlarged), Entrerian forma- 

 tion, e-k. Younger beds, Seymour Island, off Graham Land, Antarctica (after 

 Buckman), (natural size), e. B. ovalis Buckman. /, j, h. B. antarctica Buckman. 

 g. B. elliptica Buckman. h. B. angusta Buckman. i. B. attenuata Buckman. 

 f I l. ? B. rosea (Mawe), Becent, Brazil (after Davidson). 



Fig. 5. — Rhizothyris rliizoidu (Hutton). a. Holotype, Mount Brown beds, Weka Pass 

 (specimen in the Canterbury Museum). 6. Interior of dorsal valve, Weka Pass, 

 c. Interior of dorsal valve, Huchinson's Quarry, d. Form with nearly straight 

 sides, Weka Pass. (Figs, a-c by Dr. C. A. Cotton.) 



and beak characters, and, if this be so, we must be dealing with a third 

 stock which has attained independently the Magellaniform loop. In any 



