Fossil Phyllopoda. 287 



the expedition with the CJiallenger. An opportunity 

 so favourable and important may never occur again. 

 " Ever glad to hear from you, with kind regards, 

 " I remain yours, 



" DAVID ROBERTSON.'' 



While working at sea-weeds, shells, nudibranchs, 

 amphipods, and various smaller fry, he was still 

 keenly engaged upon geological studies. Writing 

 in this same month to Mr. Neilson in regard to the 

 carboniferous shales near Glasgow, he says, " I may 

 mention that Mr. Young and I were very fortunate 

 at East Kilbride. He got a fine Dithyrocaris and 

 I got another. One of them is certainly a species 

 new to science." The specimens referred to belong 

 to a genus of fossil crustaceans, and of this very genus 

 no less than three new species were described in the 

 following year by Henry Woodward , and Richard 

 Etheridge, Junr., as derived from the lower carboni- 

 ferous limestone in the locality above mentioned. 



To Mr. W. Percy Sladen, a great authority on 

 echinoderms, with whom eventually he became very 

 intimate, he wrote a letter on September 16, 1873, * n 

 regard to the discovery of a little sea-urchin, Echinus 

 mglectus, in an unexpected locality : 



" An animal may be abundant, and yet, from the 

 nature of its habitat, or the want of knowledge of 

 the tackle proper to secure it, it may for long be 

 considered to be rare. For example, Pecten septem- 

 radiatus has long been considered a rather rare shell 

 in the Clyde district. Some years ago 1 was dredging 

 in Loch Fyne. I said to my boatman, when speaking 



