336 
THE VOYAGE OF H.M.S. CHALLENGER. 
Ammodiscus spectabilis, H. B. Brady (Pl. XXXVIII. figs. 20-22). 
Ammodiscus spectabilis, Brady, 1881, Quart. Journ. Micr. Sci., vol. xxi. N. S., p. 51. 
Test free ; composed of a non-septate tube wound upon itself, not regularly and 
symmetrically, so as to retain a rectilinear contour (as in Ammodiscus shoneanus), but in 
curved or twisted fashion, so as to form an arcuate or subhelicoid test. Shell-wall very 
thin ; exterior somewhat rough, interior smooth and polished. Longer diameter, -1-th inch 
(5 mm.) or more. 
It has not been without considerable hesitation that this form has been allotted a 
place amongst non-septate Trochamminince. In the general contour and arrangement of the 
test, it resembles such species as Ammodiscus shoneanus and Ammodiscus gordialis, and 
there is no other group of Foraminifera with which it appears to have any particular 
affinity. On the other hand, the organism is altogether larger than any of its congeners, 
and the test, though thin, is comparatively rough externally. There is perhaps no 
Foraminifer of similar dimensions of which the investment is so thin and fragile ; it is 
in fact little more than a chitinous membrane sprinkled with sand, with just sufficient 
calcareous cement to prevent it collapsing on being dried. 
The drawings of this species are from specimens in Dr. Carpenter’s collection, obtained 
on the “ Porcupine ” Expedition, — North Atlantic, 358 fathoms. Some broken tests, 
which when living must have possessed similar characters, though they are now too 
much injured to be identified with certainty, have been picked out of dredged materia] 
from one of the Challenger Stations in the South Atlantic, — east of Buenos Ayres, 1900 
fathoms. These scanty items are the extent of our knowledge of its distribution. 
Trochammina, Parker and Jones 
Nautilus, pars, Montagu [1808], Pennant, Turton. 
Eotalina, pars, Williamson [1858], Alcock, Parfitt. 
Trochammina, Parker and Jones [1859], Reuss, Carpenter, Brady, Karrer, Miller and Vanden 
Broeck, Schulze, Robertson, G. M. Dawson, Berthelin, Siddall, &c. 
Rotalia, pars, Morris and Quekett [I860]. 
Test free or rarely adherent, convoluted ; Eotaliform, nautiloid, or irregularly coiled, 
more or less distinctly segmented. Walls thin, composed of minute sand-grains, either 
incorporated by calcareous or other cement, or embedded in a chitinous membrane ; 
exterior smooth, often glossy; interior smooth, rarely punctate or reticulate, never 
labyrinthic. 
The generic term Trochammina in its restricted sense is employed for all the 
convoluted modifications of the type that are distinctly segmented; whether they are 
