1893.] Ontogeny and Phylogeny in the Brachiopoda. 601 
the form and disposition of the brachia and their supports. 
The highest genera in one subfamily, which is austral in dis- 
tribution, pass through stages correlated with the adult 
structure in the genera Gwynia, Cistella, Bouchardia, Megerlina, 
Magas, Magasella, and Terebratella, and reach their final develop- 
ment in Magellania and Neothyris. The higher genera in 
another subfamily, boreal in distribution, pass through meta- 
morphoses correlated with the adult structures of Ghwynia, 
Cistella, Platidia, Ismenia, Mühlfeldtia, Terebratalia, and -Dallina. 
'The first two stages in both subfamilies are related in the 
same manner to Gwynia and Cistella. The subsequent stages 
are different except the last two, so that the Magellania 
structure is similar in all respects to the Dallina structure, 
and Terebratella is like Terebratalia. Therefore, Magellania and 
Terebratella are respectively the exact morphological equiv- 
alents to, or are in exact parallelism with Dallina and 
Terebratalia. 
The stages of growth of the genera belonging to the two sub- 
families Dallininæ and Magellaniine are further correlated in 
the accompanying tables. 
The simplest genus, Gwynia, as far as known, passes through 
no brachial metamorphoses, and has the same structure 
throughout the adolescent period, up to and including the 
mature condition. In the ontogeny of Cistella, the gwyniform 
stage, through acceleration, has become a larval condition. 
In Platidia, the cistelliform structure is accelerated to the imma- 
ture period, and in Ismenia (representing an ismeniform type of 
structure in the higher genera), the gwyniform and cistelliform 
stages are larval, and the platidiform represents an adolescent 
condition. Similar comparisons may be made in the other 
genera. Progressively through each series, the adult structure 
of any genus forms the last immature stage of the next higher, 
until the highest member in its ontogeny represents serially, 
in its stages of growth, all the adult structures, with the larval 
and immature stages of the simpler genera. It is evident that 
in the identification of species belonging to the Terebratel- 
lide, whether recent or fossil the strict specific characters 
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