398 C. E. JBeecher — Development of Terehratalia ohsoleta, Dall. 



Figs. Ed, Fd, Gd. — The same stages in Terebratella rubicunda G. B. Sowerby. 

 Fig. E. — Magas pumilus Sowerby, the Cretaceous prototype of this structure. 

 Figs. Ef, Fe. — The magadifonn and magaselliform stages of Magasella Cuming ^ 



Davidson. 

 Fig. Db. — Megerlina Lamarckiana Davidson, adult form of brachial supports. 

 Fig. Cb. — Kraussina rubra Pallas, adult, showing septum and two branches. 

 Fig. Cc. — Kraussina pisuni Val. apud Lam, 

 Fig. Cd. — Bouchardia rosea Mawe, adult, showing thickened cardinal process^ 



hinge plate, and ring on the septum as in Ca. 



PLATE II. 



Fig. 1. — Brachial supports of Macandrevia cranium, nearly adult, p, p, points 



of former attachment to a septum in terebratalifortn stage. Enlarged. 

 Fig. 2. — Dorsal valve of TerebratuHna septentrionalis Couth., with cirrated bra- 



chia attached, showing relations of calcareous loop, which is darkly shaded 



in the drawing. 

 Fig. 3. — Dorsal valve of Magellania kerguelenensis Davidson, with cirrated bra- 



chia attached, showing relations of calcareous loop, which is darkly shaded 



in the drawing. 



Terebratalia obsoleta Dall. 



Fig. 4. — Loop in late platidiform stage, with cirrated margin of lophophore 

 attached, x 15. 



Fig. 5. — Side view of lower half of preceding, showing cirrated edge of lopho- 

 phore passing from the descending branch of loop to septum, and over 

 ascending branch, x 15. 



Fig. 6. — Dorsal view of adult shell. Natural size. 



Fig. 7. — Exterior of ventral valve. Natural size. 



Fig. 8. — Profile showing relative convexity of valves. Natural size. 



Fig. 9. — Front view. Natural size. 



Fig. 10. — Early larval brachiopod, interior of dorsal valve, showing the incom- 

 plete circlet of tentacles or cirri, visceral mass, and some of the muscles ; 

 tl, tV, first tentacles developed ; t2, t2', second pair of tentacles ; tS, td'; 

 third pair of tentacles; 14, f4', last pair; t5, new tentacle just growing 

 on one side of median line ; m, mouth ; ds, dental sockets ; did, diductor 

 muscles ; ad, adductor muscles, x 90. 



Figures 10, 11, 12, are drawn from specimens which had been dried and 

 afterwards expanded by soaking in water, and then stained and prepared 

 for mounting. The original proportions and relations of parts may be 

 therefore somewhat altered. 



Fig. 11. — Gxvyniform stage, showing complete circle of cirri; ps, pallial sinus, 

 se, setae in edge of shrunken mantle, x 60. 



Fig. 12. — Cistelliform stage, showing deflection of growing cirrated edge of 

 lophophore by dorsal septum, s; m, mouth; ad, adductor muscles; did, 

 diductor muscles ; ds, dental sockets, x 60. 



