192 Rf'porfs and Proceedings — Geological Society of London. 



The relations between the crystalline limestones and nepheline- 

 syenites of Alno have suggested to Professor Hogbom that perhaps 

 the limestones may have been a product of the nepheline-syenite 

 magma there. 



The author feels sure that the crystalline limestones of Ceylon 

 have not arisen by the alteration of the basic lime-silicates of the 

 pyroxene-granulites, although Professor Judd has advanced this 

 theory in connection with the crystalline limestones of Burma, 

 which seem to resemble those of Ceylon in many ways. 



2. " On Proterozoic Gasteropoda which have been referred to 

 Murcliisonia find Pleurotomnria, with Descriptions of New Subgenera 

 and Species." By Miss Jane Donald. (Communicated by J. G. 

 Goodchild, Esq., F.G.S.) 



Many of the Palaeozoic shells referred to Murchisonia do not 

 agree with the type, and there are at least two separate groups 

 distinguished by the outer lip. The typical' growth has a slit, the 

 other merely a sinus. As the outer lip is rarely well preserved, it 

 is difficult and sometimes impossible to decide whether a particular 

 individual belongs to one or other of these two types. With 

 regard to these shells, two important questions require to be 

 answered. Firstly, whether the slit or the sinus characterizes 

 the more primitive type ; and secondly, whether the elongated 

 Murchisonia and the shorter JPleurotomaria are both derived from 

 the same stock, and which of them appears the earlier. Before 

 considering the British evidence the work of foreign palceontologists 

 is reviewed by the authoress. From the material at present available, 

 in the British Isles as well as in America and the Baltic Provinces, 

 elongated forms with a sinus precede those with a slit. There are 

 at least two distinct groups of sinuated shells with a band : one, 

 containing Hormotoma, SJctomaria, etc., having the lines of growth 

 sweeping back to and forward from the band very obliquely ; and 

 a second, containing LopJwspira, having the lines less oblique and 

 agreeing more in direction with those of Murchisonia, only the band 

 is prominent instead of being grooved. A possible third group is 

 indicated by a subgenus, subsequently described, in which the lines 

 of growth are but slightly oblique and the band grooved. The 

 first two groups in Britain range from Upper Cambrian to Silurian 

 rocks, and the third from the Bala to the Silurian. The genus 

 Murchisonia may have begun in the Wenlock formation. So far, 

 no light is thrown on the question as to whether Murchisonia and 

 Pleurotomaria were derived from the same stock, nor has the 

 authoress yet met Avith any specimens showing a transition from 

 sinus to slit. 



In the latter part of the paper three new subgenera, eleven new 

 species, and one new variety are described and figured. 



