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Dr. J. Allan Thomson—On the Terebratellidcee. 497 
dental plates in the Dallinine and the relationships of Miuhifeldtia. 
These observations pave the way for a further advance in the natural 
or genetic grouping of species and genera. At the same time, while 
admitting that Dallina is ventrally biplicate, I am not disposed to 
agree with Mr. Jackson that the folding is exactly comparable to the 
ventral biplication exhibited in some species of MMagellania, but 
probably arose in a different way. I refrain from a further 
statement on this point, as I understand that Mr. 8. S. Buckman is 
discussing the subject of types of folding fully in his forthcoming 
memoir on the Jurassic Brachiopods of Burma. In what follows 
I shall have again, through lack of specimens in Colonial museums, to 
rely on figures to some extent, and may possibly again err from this 
cause, and if so hope the correction will be applied as promptly and 
informatively as in the former case. 
Primary Divisions oF THE TEREBRATELLIDS. 
Beecher, in 1895, recognized three subfamilies within the 
Terebratellide, distinguished by loop characters and development, 
viz.: the Megathyrine, the Dallinine, and the Magellanine. In 
1897 Schuchert included besides these three also the Devonian 
Tropidoleptine, but in 1913 he relegated this subfamily to the 
Strophomenide, with the other members of which it agrees more 
nearly in geological age, and retained in the Terebratellide only 
the three subfamilies adopted by Beecher, whose epoch-making 
classification has thus stood the test of time for twenty-one years. 
Certain minor modifications of Beecher’s statement of the order of 
loop development in the higher subfamilies of the Dallinine and 
Magellanine have become necessary owing to the re-naming and 
closer definition of some of the genera on which he based his terms. 
The following table shows the former and the revised nomenclature :— 
STAGES OF LOOP DEVELOPMENT IN TEREBRATELLIDS. 
DALLININE. MAGELLANINE. 
Revised Revised 
Beeeher,-1895. Nomenclature. Beecher, 1895. Nomenclature. 
Bouchardiform Preandee 
Platidiform. Platidiform. Megerliniform eae Ora 
Ismeniform. Ismeniform. Magadiform. Magadiniform. 
Mihlfeldtiform. Frenuliniform. Magaselliform. Magelliform. 
Terebrataliform. Terebrataliform. | Terebratelliform. | Terebratelliform. 
Dalliniform. Dalliniform. Magellaniform. Magellaniform. 
The reasons for an alteration of the terms applied to early stages of 
Terebratella and Magellania have been fully explained in former 
papers (Thomson, 1915, Nos. 2 and 3). The substitution of 
‘Frenuliniform ’ for ‘Mihlfeldtiform’ has been proposed by Jackson 
(1916) on the ground that Mihifeldtia belongs to the Magellanine 
and not to the Dallinine. In any case ‘F renuliniform’ is the 
DECADE VI.—VOL. II.—NoO. XI. 32 
