[ viii ] 
XX. Examination of the proximate Principles of some of the Lichens. — Part II. Bp 
John Stenhouse, F.R.S 393 
XXI. On the Structure of the Dental Tissues of Marsupial Animals, and more espe- 
cially of the Enamel. By John Tomes, Surgeon-Dentist to the Middlesex 
Hospital. Communicated by R. E. Grant, M.D., F.R.S., Professor of Com- 
parative Anatomy and Zoology at University College 403 
XXII. On the Anatomy and the Affinities of the Family of the Medusae. By Thomas 
Henry Huxley, Esq., Assistant -Surgeon of H.M.S. Rattlesnake, now engaged 
in a Surveying Voyage conducted by Capt. Stanley on the Coasts of Australia 
and New Guinea. Communicated by the Bishop of Norwich, F.R.S. . 413 
XXIII. On the Microscopic Structure of the Scales and Dermal Teeth of some Ganoid 
and Placoid Fish. By W. C. Williamson, Esq. Communicated by Dr. Lan- 
kester, F.R.S 435 
XXIV. On theNitroprussides, a New Class of Salts. By Dr. Lyon Playfair, F. R.S. 477 
Index 519 
Appendix. 
L J ] 
Presents 
