450 PERCY SLA DEN TRUST EXPEDITION 



these large specimens from the Indian Ocean are merely large or hypertrophied specimens 

 of Polytrema, and even after observing the difference in structure between them and 

 Polytrema I considered the possibility that they may have passed through either a 

 Polytrerna-Bta,ge or a Homotrema-$,ta,ge. 



Two facts seem to render any such view quite untenable. There is a small branch 

 of some dead coral in the collection to which are attached in close proximity a specimen 

 of Homotrema 5 "25 mm. in height and 5 mm. in diameter at the crown, and a young 

 specimen of Sporadotrema 3"25 mm. in height and T75 mm. in diameter. Both of these 

 specimens show the surface characters of their respective genera with great distinctness, 

 although the Sporadotrema is actually smaller than the Homotrema. 



In the section of the initial chambers of the specimen of Sporadotrema from 

 Providence the central chamber is 0'33 mm. x 0'48 mm. in measurement. In Polytrema 

 miniaceuvi the average diameter of the central chamber of ten specimens is 0051 mm. 

 according to Lister (11), but the average diameter of eleven specimens in the Halkyard 

 collection I have found to be about 0'075 mm. 



The description of the structure of Sporadotrema for comparison with that of 

 Homotrema and Polytrema on pp. 445 and 447 is as follows. 



The surface of the stem and, in many cases, of the proximal parts of 

 the branches as well are not marked by areolae at all. The foramina are 

 scattered irregularly on the surface and are of relatively large size. There are 

 no pillar pores. Below the surface there may be seen a number of chambers 

 communicating with one another by large open passages and bounded by 

 solid walls. There are no hollow pillars and no foramina except those on 

 the outer walls of the superficial chambers (Plate 32, figs. 20, 21 and 26). 



III. ON THE GENERIC AND SPECIFIC NAMES. 



There can be no doubt that Pallas, one of the earliest writers on these corals, 

 examined specimens of both the genera Polytrema and Homotrema. The distinction 

 he draws between the colour of his Mediterranean specimens and the colour of those 

 from the American sea, together with his special description of the form of the 

 American variety, indicate this with sufficient clearness. It is therefore a matter of 

 choice, governed by no special rule of nomenclature, which genus shall retain the 

 original name. It will be doubtless the more convenient plan to assign to the very 

 common Mediterranean foraminifer which has been so well described by Max Schultze 

 and Merkel the generic name Polytrema. 



In selecting a name for the specimens from the American seas and elsewhere which 

 I have shown to be distinct I have chosen the generic name Homotrema, signifying 

 "pores together" (cf. 6/x6aTTopo<; = sown together) with reference to the character that the 

 foramina are confined to defined areas on the surface. For the third genus which is 

 characterised by the fact that the foramina on the surface are relatively few in number 

 and are scattered without reference to any defined areas I propose the generic name 

 Spwadotrema. 



The questions of the specific names present some difficulties. It is clear that the 



