Reports and Proceedings — Geological Society of London. 135 



poiuts from 8 to 18 centimetres apart, and when they had grown to 

 some size a second crop of smaller crystals grew at nearer points ; the 

 magnetite was much aggregated round the plagioclase-phenocrysts, 

 growing together with the plagioclase of the groundmass ; and finally 

 the remaining magma crystallized. The order of crystallization is 

 found to be consonant with the phj'sico-chemical laws applying to the 

 phase liquid-solid. Graphic representations are given to illustrate 

 the order of crystallization of a ternary system of plagioclase, 

 magnetite, and pyroxene ; and it is shown that the separation of 

 such a system would yield first the formation of plagioclase-pheno- 

 crysts ; secondly, the solidification of a magnetite-plagioclase eutectic; 

 and finally an eutectic of plagioclase, magnetite, and pyro.x;ene. In 

 considering the equilibrium between the solid and the liquid albite- 

 anorthite phase, it is found that equilibrium must have been 

 maintained sufficiently long for the phenocrysts to acquire a com- 

 position different from the first-formed crystals, but that eventually 

 the equilibrium broke down, a matter possibly connected with the 

 size of the phenocrysts in relation to the viscosity of the solution. 

 The history of events in connection with the pyroxenes was probably 

 similar to that in the case of the plagioclases, but this portion of the 

 subject is not fully worked out. The temperature interval of crystal- 

 lization is estimated to have been between about 1400° and 1000°. 



The author considers that this investigation establishes that the 

 processes of crystallization in a magma may be explained in all 

 details according to physico-chemical laws. 



2. " On the Genus Loxonema, with Descriptions of New Protei'ozoic 

 Species." By Mrs. Jane Longstaff {;nee Donald), F.L.S. (Communicated 

 by Dr. G. B. Longstafi", M.A., F.G.S.) 



There is some confusion with regard to the type of the genus 

 Loxonema, which has arisen from the confounding of the Silurian 

 Terebra (?) stnuosa of Sowerby with the Devonian form which Phillips 

 called L. sinuosum. This matter is discussed, and the author, following 

 Lindstrom, Koken, and Perner, takes Z. sitiuosiwi, Sowerby, as the 

 type in the absence of sufficient reasons to the contrary. If this be 

 done, the other two types mentioned by Phillips cannot remain in the 

 genus, one belonging to the genus Macrocheilina and the other to 

 Zygopleura. This paper deals simply with Ordovician and Silurian 

 species, therefore only a few subgenera are referred to — Rhahdostropha, 

 Don., and Stylonema, Perner. 



The diagnosis of Loxonema is amended, and a note given as to the 

 true range and the geographical distribution of the genus. Descriptions 

 are given of L. sinuosum, Sow., of L. intumescens, Lindstr., and of 

 L. striatissimum, Salt. MS., and six new species and one new variety 

 are described of this genus. R.pseudofasciatnm., Don., and R. Grindrodi 

 and a new species of this subgenus from Stoke Wold in the Lower 

 Ludlow Beds are next described. This is followed by a description of 

 two new species of the subgenus Stylonema, one from the Chair of 

 Kildare and the second from Mulloch Hill. In conclusion, a new 

 species of Sormotoma from the Llandeilo Flags of Builth Bridge is 

 described. * 



