Zoological Society. 229 



usually occur in bundles, each crystal, like a thin needle, being 

 very slender, long, and pointed at the ends. Unlike sphse- 

 raphides, the bundles of raphides are easily broken up, so that 

 these crystals are most readily seen swimming freely and sepa- 

 rately in the field of vision, though it is often difficult, if not im- 

 possible, to see on them any sharp edges or flat faces. But some- 

 times the crystals are larger and their shape very obvious, of 

 which instances occur in some Liliaceae (as Yucca) and in most 

 Iridacese. These crystals are regular prisms, that is to say, with 

 three parallel angles and faces, so that a transverse section thereof 

 would be an equilateral triangle. They are also very long \\\ 

 proportion to their thickness, yet comparatively thicker than the 

 acicular forms ; and their ends are either abrupt or sharply 

 pointed. Besides, these crystal prisms generally, if not regularly, 

 appear either singly or in pairs, and are with difficulty detached 

 from the tissue of the leaf in which they are imbedded, thus 

 differing remarkably from the more slender fasciculated raphides. 

 When we do succeed in getting the crystal prisms to float freely 

 in the field of vision, they are seen to be beautiful objects ; and 

 it is probable that they might prove useful in experiments on 

 the refraction, polarization, and decomposition of light. I have 

 chiefly examined them in Iridacese, in which order they occur 

 abundantly, as may be well seen in difi'erent species of /m, 

 Trichonema, Crocus, and Gladiolus. In the leaves of the com- 

 mon and showy cottage favourite with large blue or purple 

 flowers [Iris germanica ?), the crystal prisms are quite as distinct 

 as in any of the British plants; so that even humble town 

 gardens may afford subjects for observations on these prisms 

 when the more fugitive leaves of other genera of the order have 

 disappeared. 

 Edenbridge, August 6, 1863. 



PROCEEDINGS OF LEARNED SOCIETIES. 



ZOOLOGICAL SOCIETY. 



Jan. 13, 1863. — George Busk, Esq., F.R.S., in the Chair. 



Contributions to the Knowledge of the British 

 Charrs. Part II. By Albert Gunther, M.A., Ph.D., 

 M.D., F.Z.S. 



Since the publication of my first paper on this peculiar group of 

 Salmonidcs*, I have received very valuable materials for prosecuting 

 my researches. The additional specimens show that I have been 

 correct in distinguishing the three British species from those of the 

 Continent and from one another, and that the differences between 

 * ' Annals,' Sept. 1862, p. 228. 



