382 Reports and Proceedings — The Royal Society. 



Lepidodendron fidiginosum, Will., a structural species, appears to 

 include a specimen the external structure of which corresponds with 

 Lepido2)hloios acerosus, Lepidodendron obovatum, L. aculeatum, and 

 Sigillaria discophora. Under these circumstances, it is proposed to 

 take no account of the impression-species in considering the synonymy 

 of the structural specimens, and vice versa. When the exterior of 

 a structural specimen is actually known, it may be referred to by the 

 name of the structural species, with that of the impression-species 

 added in brackets. 



Dr. G. r. Herbert Smith, M.A., F.G.S., exhibited two forms of 

 refractometer. The one (which reads directly to the second, and by 

 estimation to the third, place of decimals) has a range extending 

 from 1-300 to 1'795, and is intended for all translucent substances, 

 especially minerals. The other (which reads directly to the third, 

 and by estimation to the fourth, place of decimals) has a range 

 extending from 1-3200 to 1-4200, and is intended for use with 

 water and solutions in water, especially brines, for which reason it 

 may be called a salinometer. The liquid film is illuminated from 

 above, and the optical arrangements are such that the critical edge 

 is blue, if coloured at all, in white light. Since the refractive 

 indices of liquids change rapidly with the temperature, a water-jacket 

 is provided for controlling the temperature of the observation ; 

 a thermometer, reading to degrees Centigrade, is attached underneath 

 the instrument. The glass prisms are removable for cleaning purposes. 



The next meeting of the Society will be held on Wednesday, 

 IS'ovember 3, 1909. 



III. — The Eoyal Society. 



Oedikaey Meeting, June 24, 1909. — Professor J. Cossar Ewart, 

 Vice-President, in the Chair. 



"The Possible Ancestors of the Hoeses living under Domesti- 

 cation." Part I. By J. C. Ewart, M.D., F.R.S. 



By some naturalists it is believed that domestic horses are the 

 descendants of a Pleistocene species {Eqims fossilis), now represented 

 by the wild horse {E. przetvaUkii) of Mongolia ; by others the horses 

 living under domestication are said to be a blend of a coarse-headed 

 northern species allied to Prejvalsky's horse and a fine - limbed 

 southern species which in prehistoric times inhabited North Africa, 

 or a blend of a Prejvalsky-like northern species and a southern species 

 closely allied to E. sivalensis of the Pliocene deposits of India. The 

 examination of the skull, teeth, and limb bones of horses found at 

 Roman settlements and in the vicinity of pile dwellings indicates 

 that domestic horses originally belonged to several distinct types, 

 viz. (I) a type characterized by long limbs, by a long face, broad 

 and convex between the orbits, and strongly deflected on the cranium, 

 and by the crown of the fourth premolar being from before backwards 

 about 2-5 times the length of the grinding surface of its 'pillar'; 

 (2) a type with slender limbs, a fine, narrow, slightly deflected face, 

 and the crown of the fourth premolar about three times the length 

 of its 'pillar'; (3) a type with fairly slender limbs, a long, narrow, 



