Yol. 62.] BRACHIOPOD HOMOEOMORPHY. 453 



Bifidate Stage. 



Fig. 2. Antinomia sima (Zeuschner) (Pictet), after Pictet. — a, Ventral valve, 

 showing arrested median lobe and growth of lateral lobes ; b, lateral 

 view showing curved side-margin, (p. 441.) 



3. Antinomia diphora (Zeuschner) ?, after Pictet. (p. 441.) 



4. Antinomia sp. a, after Pictet. — A form showing the lobes becoming 



approximate, (p. 442.) 



Perforate Stage. 



5. Antinomia dilatata, Catullo, after Pictet.— a, Dorsal valve; b, lateral 



view of another specimen, showing the much curved side-margin, 

 atter Suess. (p. 442.) 



6. Antinomia cor (Bruguiere), after his fig. in the Journ. d'Hist. Nat. 



(p. 442.) 



7. Antinomia angusta, Catullo, after Pictet. (p. 443.) 



The above three forms (figs. 5-7) are arranged obliquely, because, 

 according to the principles of tachy genesis, it does not seem possible 

 for the latangulate form (fig. 5), with its continued increase of 

 expansion, to have passed into the angustangulate form (fig. 7). Nor 

 does it seem possible for a narrow form like fig. 7 to have expanded 

 sufficiently to produce a form like fig. 5. Perhaps the forms (figs. 5-7) 

 are developments of a common intermediate form. 



Imperforate. 



8. Antinomia pileus (Bruguiere).— a, Dorsal valve, after his fig. in the 



Journ. d'Hist. Nat. ; b, ventral valve of another specimen (after 

 Pictet), showing a return to the linguiform depression of the 

 glossothyridoid stage ; c, end-view of another specimen, dorsal 

 valve uppermost, after Quenstedt, showing a broad linguiform 

 depression, (p. 444.) 



Perforate— Securiform. 



9. Antinomia cf. triquetra (Parkiuson), after Pictet. — a, Ventral valve ; 



b, lateral view, showing a margin curved, but less so than in fig. 5 b. 

 (p. 443.) 



Figs. 10-16. Pygope. 

 B i f i d a t e. 



10. Pygope sp:, after Pictet, pi. xxx, fig. 5 : morphic equivalent of 



Antinomia simaand A. diphora (figs. 2 &3).— a. Ventral valve showing 

 latangulate form ; b, lateral view, showing almost straight margin. 

 (p. 445.) 



Perforate. 



11. Pygope sp., after Pictet, pi. xxix, fig. 6 a. — A form showing the lobes 



just joining up. (p. 445.) 



12. Pygope janitor, Pictet, after his figure (pi. xxx, fig. 2 Ms). —Dorsal 



valve of a latangulate form, morphic equivalent of Antinomia 

 dilatata (fig. 5), but showing a remarkable difference in the size of the 

 perforation, (p. 445.) 



13. Pygope deltoidea (Valenciennes), after the figure in the Ency. Meth.— 



A form with the anterior angles rounded off. I have placed it 

 directly above fig. 11, of which it seems to be the further direct 

 development. It can hardly have come through P. janitor, fig. 12. 

 (p. 445.) 



14. Pygope Duvali, Newman, atter his figures in the ' Zoologist.'— a, Dorsal 



valve ; b, lateral view showing straight margin. This seems to be a 

 sort of dwarf P. janitor, (p. 446.) 



