No. XX.— ON POLYTREMA AND SOME ALLIED GENERA. A STUDY OF 

 SOME SEDENTARY FORAMINIFERA BASED MAINLY ON A COLLEC- 

 TION MADE BY PROF. STANLEY GARDINER IN THE INDIAN OCEAN. 



By Sydney J. Hickson, F.R.S., Professor of Zoology in the University of Manchester. 



(Communicated by Prof. J. Stanley Gardiner, M.A., F.R.S., F.L.S.) 



Read 4th May, 1911. 

 (Plates 30—32 and one Text -Figure.) 



I. INTRODUCTION. 



Some years ago Professor Stanley Gardiner sent to me a small collection of 

 Stylasterina from the Indian Ocean for investigation and description; but I found 

 included in the consignment some purple and yellow corals which, having a superficial 

 resemblance to some varieties of Distiehopora, might easily be mistaken for Stylasterina 

 in the process of sorting out the specimens of such a large collection as Prof. Gardiner 

 made in the course of his expedition. Having no special knowledge of the Foraminifera 

 it did not occur to me at once that these large dark red and yellow corals could have any 

 relation to the well-known genus Polytrema, but further investigation convinced me that 

 the specimens were identical with or closely allied to the specimens collected in the Gulf 

 of Manaar by Captain Warren and described by Carter (5) as Polytrema cylindricum. 



Carter's description of his new species was very brief and I found it very difficult to 

 understand the reason for including it in the genus Polytrema, as there are many characters, 

 apart from its great size and its colour, in which it differs from the Polytrema miniaceum 

 that is found in the Mediterranean Sea and elsewhere and is so well known to zoologists 

 by the researches of many investigators. I endeavoured, therefore, in the first place to 

 clear my mind as to the essential characters of the genus Polytrema; but, on reference 

 to the literature, I came across a great difficulty which it took me some time to unravel. 



The accounts given of the structure of Polytrema by different authors of repute are 

 not consistent, and the inconsistencies cannot be accounted for by any supposition that 

 they are due to gross inaccuracy of observation and description. 



Fortunately there is in the Manchester Museum the large and valuable collection of 

 Foraminifera made by Mr E. Halkyard and included in this collection are several specimens 

 of Foraminifera labelled Polytrema miniaceum. On making a careful examination of one 

 series of specimens in this collection from the West Indies I found that the structure of 

 the surface corresponds very closely with the description given by Carpenter and is totally 

 different to that given by Max Schultze, Merkel and Lister, but on the other hand the 

 descriptions given by Max Schultze, Merkel and Lister agree quite accurately with the 

 structure I was able to observe on the specimens collected at Nice and from a locality off 

 the Kermadecs in the S. Seas. 



