67 
MICROSOPICAL AND NATURAL HISTORY SECTION. 
12th February, 1883. - 
James Cosmo Melyill, M.A., F.L.S., President of the 
Section, in the Chair. 
The Secretary announced the presentation to the Section 
by T. R. Archer Briggs, F.L.S., of a copy of his “ Flora 
of Plymouth,” and by Messrs. Melvill and Bailey of the 
“Journal of Botany,” in monthly parts as issued. 
Mr. J. C. Melyill exhibited a dwarf specimen of the 
common Harebell Campanula Rotundifolia, having the 
corolla divided into five equal lingulate segments down 
to the base, found on Afton Down, Isle of Wight. 
Also specimens of Calamintha Sylvatica, Blomfi, and Cam- 
panula Glomerata, L., var. Nana Bailey, and of Erythrsea 
Capitata, Wiild., var. Sphserocephala, Townsend, one of the 
rarest British plants. 
Dr. Alcock read a paper on the Structure of the Shells 
of several common species of Polymorphina, and exhibited 
specimens and drawings to illustrate his remarks. He 
showed, by transparent specimens mounted in balsam, that 
in all cases the walls of the inner chambers which have 
become enclosed by later growths are to a considerable ex- 
tent removed by absorption, opening out the interior into 
one large cavity, and that in P. oblonga and P. gibba this 
absorption is remarkably well seen. 
By endeavouring to form an idea of the mode of growth 
of these shells in relation to the life of the contained animal, 
he had been led to doubt the distinctness of P. lactea and 
P. compressa as species, the former apparently being P. 
compressa in the young state ; and he could not avoid the 
