Bd. III: 9) 
THE Fossil, FORAM INIFER A. 
3 
number and slightly embracing. Aperture crescentic. Texture very finely arenaceous, 
exterior smooth. Diameter, of the specimen described, 4 mm. 
This species bears a close relation to the common Ammodisats incertiis, 
(d’Orbigny) but it differs from that form by the small number of its convolutions 
in relation to its size, by its thicker test and by its large dimensions. 
Brady, in the Challenger Report' gives the range of size in Ammodiscus iuccrtus 
as from o.i mm. to nearly 3 mm. and goes on to say: — ^about 0.5 mm. is the 
average measurement of recent specimens, as found in very deep or very shallow 
water, and such shells generally consist of five or six convolutions of nearly even 
width. The exceptionally large specimens frequently met with in localities rich in 
arenaceous F'oraminifera, at depths of from 300 to 1,000 fathoms or thereabouts, 
attain a diameter of nearly 3 mm., and often present from fifteen to twenty con- 
volutions.» 
That small specimens show few convulutions of a tube of uniform size while 
large specimens present many convolutions of a tube with an exceedingly narrow 
commencement but which gradually broadens, is perhaps an exemplification of the 
dimorphism noted in many species of Foraminifera — the small specimens being 
»megalospheric» and the large specimens »microspheric» as commencing respectively 
with a large or small initial chamber. 
If such dimorphism extends to the present species the specimen figured will be 
the megalospheric form, and we may perhaps look for the discovery of the microspheric 
form with many convolutions and a gross diameter possibly even greater than the 
4 mm. of the present specimen. 
The Geological range of Aminodiscus incertus^ the nearest ally to A. grandis 
goes back to the carboniferous beds of England and it has been recorded from most 
if not all subsequent formations. Its geographical distribution in recent seas is very 
wide but it does not appear to have been found in either the arctic or the antarctic 
regions. GoËS records it »ad oras Scandinaviæ occidentales metr. 140 — 200 passim; 
diam. mm. 0.40 — i.»^ 
Genus Trochammina, PARKER & JONES, i860. 
Test free or rarely adherent, convoluted; Rotaliform, nautiloid or coiled irregularly, 
more or less distinctly segmented. Walls thin, composed of minute grains of sand 
and mud particles; exterior smooth, often glossy; interior non-labyrinthic. 
' Report Chall. Vol IX, 1S84, p. 331. 
’ Kongl. Sveiiskfi Vet. -Akademiens Handlingar. Bandet 25. N:r 9, p. 31. 
