396 C. E, Beecher — Devielopment of Terehratalia obsoleta^ Dall. 



Explanation of Plates. 



PLATE I. 



Ontogeny and Ph-ylogeny of the Terebratellidse. 



Figures represent bracliial supports in various stages of growth in different 

 genera and species. All are drawn of approximately the same length to facili- 

 tate comparison, so that in general the younger stages are much enlarged. Ver- 

 tical rows of figures connected by dotted lines indicate ontogeny as far as known. 

 Horizontal rows indicate the same growth stages of higher forms, and the adult 

 structure in genera representing these stages. All figures are of recent species 

 unless otherwise stated. 



Morphogeny of Megathyrinse. 



Fig. A. — Early larval brachiopod without calcified brachial supports, but with 

 circlet of centripetal tentacles on the lophophore. The gicynifonn stage. 



Fig. Aa. — G-wynia capsula Jeffreys, a morphic equivalent of larval stage, figure A. 



Fig. B. — Later immature stage of A, showing growth 6i septum, and consequent 

 introversion of edge of lophophore. Early cistelUform stage. 



Fig. Ba. — Zellania Hasina Moore, from the Lias, a' morphic equivalent of figure B. 



Fig. Bl. — Cistella neapolitana Scacchi, sho"\ving calcification of loop attached to 

 septum, and other adult features. 



Fig. B2. — Megathyris decoUata Chemnitz, adult shell sho\ving advance over Cis- 

 tella in the two lateral septa, thus increasing the length of the loop. 



Morphogeny of Dallininae. 



Ontogeny of Macandrevia cranium Miiller. 



Fig. A. — Gwynifonn stage. 



Fig. B. — CistelUform stage. 



Fig. CI. — Platidiform stage, showing union of descending lamellae with dorsal 

 septum. 



Fig. CI'. — Side view of septum of preceding. 



Fig. Dl. — More advanced platidiform stage, showing growth of ascending bran- 

 ches, or secondary loop. 



Fig. Dl'. — Side view of same. 



Fig. El. — Ismenifoi^m stage, with ascending branches still attached to septum. 



Fig. Fl. — Muhlfeldtifonn stage, shomng boles in ascending lamellae as in Miihl- 

 feldtia, figure F3. 



Fig. Gl. — Terehrataliform stage, Vsnih. ascending branches attached to ends of 

 descending branches. 



Fig. HI. — Final adult condition, showing absorption of septum and connecting 

 bands from descending branches. 



Fig. H2. — Adult stage of Macandrevia tenera Jeffreys. 



