Dear Darwin

I have been too busy to look over your list with requisite consideration until yesterday.

I have marked on the lists their probable depths judging from the associations of the genera.² My marks are within wide ranges.

I could come however to more likely conclusions were two points noted

1^st—the average size of the specimens & species found in each locality.

2^d The comparative abundance of specimens of each species, & their state, as indicating life & death &c

Thus the Huafo list might indicate twice the depth if the species are all very small & the specimens of Turritella few.

All such calculations, at any rate, must be only provisional, until we know the range in Depth of mollusca in the neighbouring seas.