232 Reports & Proceedings — Mineralogical Society. 



The examination of adult sutures of various species of Dactylioceras 

 shows that the major frillings alone are of systematic importance for 

 that genus. The variations in the minor frillings, and in the suture- 

 line as a whole, throw light on the changes which accompany senile 

 decline. 



The second septum is remarkably like the central portion of the 

 adult septum ; but the flattened portion is relatively less extensive, 

 the folds are sharper, and the whole septum tends to be concave 

 rather than convex. As development advances the successive septa 

 possess a similar resemblance to an increasing area of the adult 

 septum. The outcome of this is, that a series of septal sections of 

 the latter closely resembles the developmental series of the suture- 

 line in all three types. 



In no case do the septal sections show a stage comparable with the 

 first suture-line. In Tragophylloceras the similarity starts not later 

 than the seventh septum. With these exceptions, septal sections 

 reproduce the main features in the development of the sutures with 

 sufficient accuracy to justify their use for the same purpose, especially 

 when the material for the study of the early stages is inaccessible. 



It is possible that septal sections may also furnish the clue to the 

 probable lines along which simplification of the suture proceeds 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 two forms, 

 namely : — 



1. By the different development of the elements of opposite side. 



2. By association with the lateral displacement of the siphuncle. 



Asymmetry of the latter type has been considered as of systematic 

 importance. Nevertheless, while it does occur more frequently in 

 certain genera, as, for instance, in Psiloceras and Hoplites, it occurs 

 not uncommonly in many other unkeeled ammonites. 



III. — Mineralogical Society;. 



March 20, 1917. — W. Barlow, F.B.S., President, in the Chair. 



A. Holmes & Dr. H. F. Harwood : The Basaltic Bocks of Spitzbergen 

 and Franz Joseph Land, with conclusions regarding the Brito-Arctic 

 Tertiary Petrographic Province. These rocks, which were obtained 

 respectively from Professor Garwood and the Geological Survey of 

 England and Wales, are very similar, not only to the basaltic rocks 

 previously described from neighbouring localities, but also to the 

 basalts of the whole Arctic region stretching from Dickson Harbour 

 to West Greenland. The essential minerals are labradorite rich in 

 the anorthite molecule, pyroxene of the enstatite-augite type, and 

 titaniferous magnetite. The pi-ovince as a whole displays significant 

 variations both in time and space. The earliest eruptions are 

 generally poor in alkalies, but tend to become more alkaline as the 

 present period is approached. Thus, the later eruptions of Spitzbergen 

 gave rise to olivine trachydiorites instead of basalt. Jan Mayen still 

 possesses an active volcano, and its rocks are unusually alkaline 



