448 PERCY SLADEN TRUST EXPEDITION 



The type species has always the form of branching coralline structures but the degree 

 of ramification varies considerably in the different varieties, the details of which will be 

 related later. Flat encrusting varieties have not been found at present. 



One of the chief characters of the genus is undoubtedly the great size which it 

 attains. The largest specimen in the collection is from 70 fathoms of water off Providence 

 Island (Plate 30, fig. 3)*. It is no less than 27 mm. in height and 28 mm. in expanse. It 

 rises from a base 7x5 mm. and the diameter of the short stumpy arms is 5 — 6 mm. This 

 is truly a giant foraminifer. Selecting three fine specimens of other facies of the genus in 

 Prof. Gardiner's collection I find that a specimen of the " Amirante " facies from 32 fathoms 

 is 10 mm. in height with an expanse of 13 mm., that a specimen of the " Saya de Malha" 

 facies from 29 fathoms is 11 mm. in height with an expanse of 15 mm. and that an orange 

 coloured variety from Cargados is 16 mm. in height with an expanse of 18 mm. All 

 of these specimens are many times larger than the largest known specimens of either 

 Polytrema or Homotrerna and a great deal larger than the type specimen discovered by 

 Capt. Warren. Another very well marked character of the genus is the colour variety. 

 The type specimen from the Gulf of Manaar and the specimens from the Indian Ocean 

 which for convenience sake I call the " Amirante " facies are dark purplish red in colour 

 (Plate 30, fig. 6). It is darker and more pronounced, " saturatior " as Pallas would have 

 said, than the colour of Homotrerna and Polytrema, but still it is a red colour. The " Saya 

 de Malha " facies is a pale purplish pink (Plate 30, fig. 4) very different in tone to the pale 

 pink varieties of Polytrema, but the specimens of the " Providence " variety are yellow 

 (Plate 30, fig. 3) and a specimen from Cargados is deep orange, colours which so far as my 

 knowledge goes are quite unknown among the varieties of the other two genera. 



But size and colour, although useful as easy guides to identification and valuable as 

 supplementary characters are not by themselves trustworthy characters upon which to 

 base a generic distinction. 



A careful examination of the structure of the specimens proves that these specimens 

 possess other and more fundamental characters which justify the conclusion that they 

 constitute a distinct genus. 



When the surface of the stem of a Sporadotrema cylindricum is examined it is found 

 to be smooth and often porcellanous in texture but perforated by a number of relatively 

 large and scattered foramina (Plate 32, fig. 21). There are no honeycomb markings nor 

 defined areas of any kind. The foramina are all of the same kind and there is no trace of 

 anything corresponding with the pillar pores of Polytrema. The foramina at the surface 

 are very much larger than those of either of the other two genera. In the specimens from 

 Providence island the average size of these apertures is - 057 mm. in diameter. In 

 Polytrema the average size of the external openings of the foramina is 0*005 mm. and in 

 Homotrerna about 0"001 mm. 



When the branches of Sporadotrema are examined, the surface may be found 

 to be marked by a pattern of grooves bounding convex areas which correspond with 

 the subjacent chambers (Plate 31, fig. 15 and Plate 32, fig. 24). The foramina on 



* The specimen drawn in Plate 30, fig. 3, and photographed in Plate 31, fig. 10, is smaller than the largest 

 specimen in the collection. 



