i86i.] DAVIDSON ON BRACHIOPODA. 



formations above and below. But several really good judges 

 have remarked to me how desirable it would be that this 

 should be exemplified and worked out in some detail and 

 with some single group of beings. Now every one will ad- 

 mit that no one in the world could do this better than you 

 with Brachiopods. The result might turn out very unfavour- 

 able to the views which I hold ; if so, so much the better for 

 those who are opposed to me.* But I am inclined to suspect 

 that on the whole it would be favourable to the notion of 

 descent with modification ; for about a year ago, Mr. Salter f 

 in the Musuem in Jermyn Street, glued on a board some 

 Spirifers, &c., from three palaeozoic stages, and arranged them 

 in. single and branching lines, with horizontal lines marking 

 the formations (like the diagram in my book, if you know 

 it), and the result seemed to me very scriking, though I was 

 too ignorant fully to appreciate the lines of affinities. I 

 longed to have had these shells engraved, as arranged by 

 Mr. Salter, and connected by dotted lines, and would have 

 gladly paid the expense : but I could not persuade Mr. Salter 

 to publish a little paper on the subject. I can hardly doubt 

 that many curious points would occur to any one thoroughly 

 instructed in the subject, who would consider a group of 

 beings under this point of view of descent with modification. 

 All those forms which have come down from an ancient 

 period very slightly modified ought, I think, to be omitted, 

 and those forms alone considered which have undergone 



* " Mr. Davidson is not at all a full believer in great changes of species, 

 which will make his work all the more valuable." C. Darwin to R. Cham- 

 bers (April 30, 1861). 



> John William Salter; b. 1820, d. 1869. He entered the service of 

 the Geological Survey in 1846, and ultimately became its Palaeontologist, 

 on the retirement of Edward Forbes, and gave up the office in 1863. He 

 was associated with several well-known naturalists in their work with 

 Sedgwick, Murchison, Lyell, Ramsay, and Huxley. There are sixty en- 

 tries under his name in the Royal Society Catalogue. The above facts 

 are taken from an obituary notice of Mr. Salter in the ' Geological Mag* 

 zine,' 1869. 



