136 Geological Society. 
It is possible that septal sections may also furnish the clue to 
the probable lines along which simplification of the suture pro- 
ceeds in the retrogressive members of any stock. 
Asymmetry of the septum, and of the suture-line, in ammonites 
is more common than is usually supposed. It may arise in one of 
two ways, namely :— 
(1) By the different development of the elements of opposite sides, 
(2) In association with the lateral displacement of the siphuncle. 
Asymmetry of the latter type has been considered as of systematic 
importance. Nevertheless, while it does arise more frequently 
in certain genera, as, for instance, in Pszloceras and Hoplites, 
it occurs not uncommonly in many other unkeeled ammonites. ; 
May 2nd, 1917.—Dr. Alfred Harker, F.R.S., President, 
in the Chair. 
The following communication was read:— 
‘Supplementary Notes on Aclisina De Koninck, and Acli- 
soides Donald, with Descriptions of New Species. By Jane 
Longstaff (wée Donald), F.L.S. 
Since the publication of a paper by the Geological Society on 
Aclisina in 1898, a much larger amount of material has come to 
hand, which has not only added to the knowledge of the species 
there described, but has also led to the discovery of six others new 
to science. The diagnoses of these are now given, and a species 
named by Mr. H. Bolton Loxvonema ashtonensis is referred to 
this genus, as several specimens show the characteristic lines of 
growth. 
The total number of species of Aclistna is now brought up to 
twenty-two, and there are besides several varieties. The genus is 
best represented in Scotland, where the specimens are ‘generally 
remarkably well preserved, no less than thirteen having the proto- 
conch intact, drawings of which show its somewhat irregular 
character. A table is appended giving—so far as known—the 
range and localities in the British Isles and Belgium. <A small 
variety of Aclisina pulchra De Koninck appears to have continued 
for the greatest length of time, commencing in the Calciferous 
Sandstone Series, existing throughout the Lower and Upper 
Limestone Series and on into the Millstone Grit of Scotland. 
Additional observations are also made on Aclisotdes striatula 
(De Koninck), showing its variation in size and ornamentation, 
as well as its range throughout the Lower and Upper Carboniferous 
Series of Scotland, its occurrence at Settle and Poolvash, and at 
Tournai as wellas Visé. New drawings are given of De Koninck’s 
type-forms. One of these, as also a Scottish example, has the 
characteristic sinus preserved. The holotypes of the first described 
species were not originally selected: that omission is now rectified, 
with references to the collections in which they are deposited. 
