[83]

For Waterhouses views two groups must be taken, & his view must refer to species only — (though this is difficulty) for in his insistence of Bizacha, his argument applies to both species of Bizcacha.— So that in the higher groups his law applies to genera, & therefore his statement wd be that the alliance was not generic, but where genera are allied, relation not specific — I suspect requires much hesitation; can only be true by my theory owing to extinction— & Lepidosiren is exception. The most that ought to be said is that his law holds in many cases, & in two well defined groups, ie descended from distinct parent stocks.— ↘

[83v]

The rarity of intermediate existing groups depends on law of genera community of advantage causing common increase & the reverse — rarity of fossil intermediate depends on small proportion preserved.—

Lepidosiren & ornithorhynchus, descendants perhaps modified of intermediate links.