PROCEEDINGS OF SOCIETIES. 
Dustin MicroscoricaL Cius. 
April 19th, 1866. 
Dr. E. Perceval Wright exhibited portions of the ambulacral 
feet, ling membrane of the intestine, and ovaries of several 
species of Echinidw, showing the very peculiar arrangement of 
spicules which appeared to be characteristic of each. His atten- 
tion had been.called to this subject by his friend Mr. C. Stewart, 
of Plymouth, who had read a very elaborate paper on these struc- 
tures as they occur in the Regular Echinoidia before the Linnean 
Society, and from what he (Dr. Wright) had been able to observe he 
had little doubt but that the comparative form and structure of 
these spicules would be of vast importance in helping to dis- 
criminate not only between the families, but also between the 
genera of these Echinoderms. He regretted not being able to 
show a series of these preparations from Mr. Stewart himself, as 
he had at first expected, as he had not succeeded in mounting his 
specimens at all in the same manner as those he had seen prepared 
by that gentleman: but the specimens he brought to the meeting 
would still be quite sufficient to justify the remarks he had made. 
Specimens were shown of the following :—Leiocidaris papillata, 
Psammechinus microtuberculatus, Psilechinus variegatus, Toxo- 
pneustes lividus, Tripneustes ventricosus, Echinometra lucunter, 
and Acrocladia mammillata. The importance of drawing up 
diagnoses of the Genera of Echinida, not as is usually done, simply 
according to the number and position of the ambulacral pores 
and the characters of the spines, but based upon details of all 
the structures met with in the recent animal, was strongly 
insisted on. Until some such plan is adopted nothing but an 
appeal to type specimens will determine genera and species that 
have been insufficiently described, even by such authors as 
Dujardin and Hupé, Forbes, Agassiz, and others. 
Mr. Archer drew attention again to the Rhizopod he had shown 
at the January meeting, and which he referred, as yet somewhat 
doubtfully, to Difflugia corona, in order to point out a peculiarity 
