PEOCEEDINGS OF THE SOCIETY. 175 



Hickson) had given the new generic name Homotrema,* from the West 

 Indies and some other locaUties. 



The two genera conld be quite easily distinguished from each other 

 by surface examination. In Polytrema the surface was perforated by 

 two kinds of pores, the larger pillar pores (of Merkel) and numerous 

 very minute foramina. In Homotrema there were no pillar pores, and 

 the foramina were confined to small round or oval areolae which were 

 convex outwards and surrounded by perfectly solid boundaries of skeletal 

 structures. Other constant differences between the two genera were 

 described. 



Both genera seemed to be widely distributed in the Pacific and 

 Indian Oceans, and might be found side by side, but hitherto no speci- 

 mens- of Homotrema had been found in the Mediterranean Sea, where 

 Polytrema was abundant ; and no specimens of Polytrema have been 

 found in the waters of the east coast of the American Continent or in 

 the West Indies. 



Another sedentary Foraminifer described was the form previously 

 known by the name Polytrema cylindrkum Carter. This was also 

 shown to be the type of a new genus, Sporadotrema. A large collection 

 of specimens of this genus were obtained by Professor Stanley Gardiner 

 in the Indian Ocean. They were usually of great size — as compared 

 with specimens of Homotrema and Polytrema — and were frequently 

 yellow or orange in colour, although specimens of the red colour of the 

 other two genera did occur. The surface character that distinguished 

 the genus from the other two, was that the foramina were large, 

 scattered, variable in size, and were not aggregated in areolae in the 

 older parts of the stock as in Homotrema. There were no pillar pores 

 as in Polytrema. 



After a brief reference to the second species of this genus —Spora- 

 dotrema mesentericum — attention was called to some very large specimens 

 of Gypsina plana from the Indian Ocean. 



Some of the specimens of this species Avere found to reach the 

 gigantic size of four inches in diameter. They formed thin encrusting 

 sheets, layer over layer on a basis of dead coral. An examination of 

 the structure of these layers showed an extraordinary variability in the 

 size of the chambers and in other characters. This variability was in 

 all probability an adaptation to the variable nature of the substance 

 over which the specimens spread, and rendered a subdivision of the 

 species into discontinuous specific groups an impossibility, as in so many 

 other forms of sedentary life. 



Certain features of these recent sedentary Foraminifera Avere then 

 compared with those exhibited by the ancient group of fossils — the 

 Stromaioporidce — and the opinion was expressed that, in conformity 

 Avith the views of Kirkpatrick, the Stromatoporidfe were probably closely 

 related to the Foraminifera. 



In the presence of the " initial chambers " of Polytrema, Homotrema 

 and Sporadotrema, there was reason to believe that they were not 

 directly descended from a sedentary ancestor, but had secondarily 

 acquired the sedentary habit after a previous free existence. 



* Trans. Linn. Soc, 1911, 14, p. 3. 



