Geological Society of London. 285 
1891 Prof. Nicholson and Mr. Marr submitted a series of similar 
microzoa from the same district; and the author now endeavours 
to determine their specific alliances, and revises the list of those 
previously collected. He has to notice about eleven forms of . 
Primitia, Beyrichia, Ulrichia, Achmina, and Cytherella—several of 
them being closely allied as varieties, but all worthy of study as 
biological groups, such as have been illustrated from other regions 
by writers on the Ostracoda, with the view of the exact determina- 
tion, if possible, of species and genera, of their local and more 
distant or regional distribution, and of their range in time. 
2. “On some Paleozoic Ostracoda from the Girvan district in 
Ayrshire.” By Prof. T. Rupert Jones, F.R.S., F.G.S. 
This paper aims at the completion of the paleontological account 
of the Girvan district, as far as the Ostracoda are concerned; and 
follows up the researches indicated in the “ Monograph of the 
Silurian Fossils of the Girvan District in Ayrshire,” by Nicholson 
and Htheridge, vol. i. 1880. 
In about a dozen pieces of the fossiliferous shales, submitted for 
examination some few years ago, the writer finds nearly thirty 
specimens of Primitia, Beyrichia, Ulrichia, Suleuna, and Cypridina, 
which show interesting gradations of form, not always easy to be 
defined as specific or even varietal, but valuable as illustrating 
modifications during the life-history of individuals, thus often leading 
to permanent characteristics of species and genera. Like those 
formerly described in Nicholson and Etheridge’s ‘“ Monograph,” 
the specimens have all been collected by Mrs. Elizabeth Gray of 
Edinburgh. 
3. “On the Dwindling and Disappearance of Limestones.” By 
Frank Rutley, Hsq., F.G.S. 
The existence of chert between two sheets of eruptive rocks at 
Mullion Island seemed to the author to require some explanation. 
Cherts are usually associated with limestones, and the absence of 
limestones in many cases where cherts are found points to their 
removal by underground waters. The older the limestone, the 
greater the probability of its thickness having dwindled. ‘The 
thicknesses of the Ordovician, Silurian, Devonian, and Carboniferous 
Limestones seem to be in the ratio of 1: 15:15: 100. Many lime- 
stones once existing in Archean rocks may have disappeared, as 
also limestones in later rocks. 
The author comments on the difficulty of distinguishing some 
cherty rocks from felstones. 
Two Appendices are added to the paper, the first on the trans- 
ference of lime from older to newer deposits, and the second on the 
formation of nodular limestone bands. 
4. “On some Bryozoa from the Inferior Oolite of Shipton Gorge, 
Dorset.—Part II.” By Edwin A. Walford, Esq., F.G.S. 
As we pass backward in time, the characters of the two sub-orders 
Cheilostomata and Cyclostomata merge. ‘The accessory organs of 
the genus and species described in this paper illustrate this state- 
ment. The genus is named Pergensia, and the following new 
