Seymour Island, West Antarctic. 259 



" The BoucliardicB, however, may be looked at from another aspect 

 — the biological: their stage of development may be considered. 

 In this respect they are intermediate between B&uchardm found in 

 the Patagonian and in the Oligocene of New Zealand on the one hand, 

 and the living Bouchardia rosea on the other ; in fact they are, so far 

 as biological development is concerned, much more advanced than 

 the Patagonian Oligocene species, and much nearer in development 

 to the present-day form. 



"The character of t\\Q BoiichardicB is wholly against their being 

 earlier than the Boucliardice. of the Patagonian. Biologically speaking, 

 the Boucliardice of the Patagonian are earlier than the Antarctic 

 Boiichardice, for they agree with the young stage and differ from the 

 adult stages of these shells. Then the Bouchardice of the New 

 Zealand Oligocene are certainly further removed from the Antarctic 

 forms; they appear to be biologically earlier than the Patagonian 

 species." 



Recently I have been able to show * that the New Zealand supposed 

 BoiichardicB possess Magellaniform loops and septa, and further that 

 in a series of shells wdth similar beak characters there are repre- 

 sentatives with all stages of loop development between those of 

 Bouchardia and Magellania. Arguing that the constancy of beak 

 characters shows that we are dealing with a stock which has attained 

 the Magellaniform loop in its highest member by a different line of 

 ancestry from Neothyris and Magellania, I proposed new generic 

 names for representatives of each loop stage as follows : — 



Magadina : Genotype J/rt^«f?mfl iro?<;w«, Thomson. LoopMagadini- 

 form, i.e. so-called Magadiform of Beecher. 



Magadinella : Genotype Magasella woodsiana, Tate. Loop Tere- 

 bratelliform. 



Rhizothjris : Genotype Bouchardia rhi%oida, Hutton. Loop 

 Magellaniform. 



Buckman^ has since shown that in 'the position of the foramen 

 there is development from the hypothyrid, through submesothyrid, 

 mesothyrid, and perraesothyrid to the epithyrid position. In this 

 respect, therefore, Rhizothyris is less advanced than Bouchardia, and 

 does not necessai'ily belong to the same stock. The similarity 

 between them in beak chai'acters is simply that in each the foramen 

 is very advanced in position, and this may be and is the case in 

 widely different stocks. Laqueus, for instance, also possesses a 

 perraesothyrid foramen, and is certainly no close relation of 

 Rhizothyris. 



Biickraan's biological argument, therefore, is weakened by the 

 inclusion of the New Zealand species of Rhizothyris, but it still stands 

 if confined to species which there is no reason to suspect are not true 

 Bouchardice. The most primitive in shape is B. patagonica, von 

 Ihering, from the Salamancan (Upper Cretaceous) of Patagonia ; then 



^ " Brachiopod Genera: The Position of Shells with Magaselliform Loops 

 and of Shells with Bouchardiform Shape" : Trans. N.Z. Inst., vol. xlvii, 

 pp. 392-403, 1915. 



'^ S. S. Buckman, " Terminology for Foraminal Development in Terebratu- 

 loids (Brachiopoda) ": Trans. N.Z. Inst., vol. xlviii, pp. 130-2, 1916. 



