32 



On behalf of Mr. R. Lydekker, the Secretary exhibited photo- 

 gruphs of a spotted bull Tsaine or Bantin, shot by Mr. Arthur 

 Porter in the great forest of Siam in November 1908, which 

 Mr, Lydekker proposed provisionally to name Bos sondaicus 

 porteri. 



Mr, Olbeield Thomas, F.R.S., F.Z.S., exhibited specimens of 

 a new Rat which had been obtained by Mr. G. C. Shortridge 

 during the Society's collecting expedition to Central America. 

 It was distinguished as follows :— 



OtOTYLOMYS GUATEMALiE, sp. n. 



Considerably larger than 0. phylloiis, greyer in colour, and 

 with the feet parti-coloured, as in some species of Tylomys. 

 Head and body 170 mm. ; tail 161 ; hind foot 28 ; skiill 40-7. 

 Hah. Tucuru, Guatemala. Type. B. M. No. 9.6.11.13. 



Dr. F. Wood Jones, F.Z.S., gave a demonstration, illustrated 

 by specimens, models, and lantern-slides, of the method of for- 

 mation of coral islands and reefs. 



The purpose of the demonstration was to show that the 

 theories of subsidence put forward by Darwin, and of solution 

 put forward by Sir John Murray, were both untenable in the 

 light of actual facts to be observed on coral islands. 



A fresh hypothesis — that sedimentation is the most important 

 factor — was substituted for these theories ; and it was pointed 

 out that the atoll was in reality a structure analogous to the 

 Porites colonies the upper surfaces of which were made basin- 

 shaped by sediment obliterating the zooids of their central ai-ea. 



That the deposition of sediment below the " limiting line of 

 sedimentation " probably accounted for the bathymetrical limit 

 of the reef-building corals, and for the formation of sedimentation 

 banks up to that line. 



That in the making of the atoll from the basin-shaped reef the 

 winds and the waves played the greatest part, and that atoll 

 lagoons tended to shoal owing to the deposition of sediment 

 within them. 



That Le Conte in 1856 had said that barrier reefs stood out 

 from shore because they were limited on one side by the depth 

 and on the other by the muddiness of the water, and that his 

 pronouncement accorded with every known fact. 



That the question of the formation of coral structures was a 

 zoological one and was to be solved by a study of the living zooid 

 and that the chief agent inimical to the growth of the zooid was 

 the deposition of sediment. 



