438 
THE VOYAGE OF H.M.S. CHALLENGER. 
alternately at either end, is more or less planospiral and subtriangular, portions of two 
segments in addition to the final one being visible externally. The final segment is 
relatively very large, and the aperture is a marginal slit on the line of union with the 
penultimate chamber. 
This genus furnishes interesting isomorphs to certain arenaceous species ; thus, for 
example, Allomorphina trigona bears a general resemblance in form and in the disposition 
of its chambers to many specimens of Trochammina pauciloculata ; and Allornorpliina 
contraria (Haidinger’s Naturw. Abhandl., vol. iv. pi. v. fig. 7) presents a contour almost 
identical with that of Trochammina galeata. 
Until comparatively recently Allomorphina was supposed to be an exclusively fossil 
type ; but small specimens have been met with in the living condition in Challenger 
soundings from the Pacific. The genus makes its first appearance, geologically speaking, 
in the Cretaceous period, and is sparingly represented in various beds of Tertiary age in 
Central Europe. 
Allomorphina trigona , Reuss (PL LY. figs. 24-26). 
Allomorphina trigona , Reuss, 1849, Denkscbr. d. k. Akad. Wiss. "Wien, vol. i. p. 380, pi. xlviii. 
fig. 14, a.-e. 
„ cretacea , Id. 1850, Haidinger’s Naturw. Abhandl., vol. iv. p. 42, pi. v. fig. 6. 
„ trigona , Brady, 1879, Quart. Journ. Micr. Sci., vol. xix., N. S., p. 67, pi. viii. 
figs. 13, 14. 
Of the two “ species ” above referred to, the former was described by Prof. Reuss 
from fossil examples of Miocene age, the latter from specimens of Cretaceous origin ; but 
I am unable to recognise any morphological characters by which they can be distinguished 
from each other, and the day is long past for accepting difference of geological age as 
a ground of zoological distinction. Nor can I find in Tertiary specimens, kindly sent 
for comparison by my friend Dr. Karrer of Vienna, any feature by which they can be 
separated, even varietally, from those living at the present time. I have had no hesita- 
tion, therefore, in adopting for the recent specimens the name first employed for 
the species. 
Allomorphina trigona is under all circumstances a rare Foraminifer. In the recent 
state it has only been found at two Challenger Stations, namely, the Hyalonema-gromid 
to the south of Japan, depth 345 fathoms, and off Tahiti, Society Islands, 620 fathoms. 
Its geological history may be gathered from Prof. Reuss’s various memoirs. It occurs 
as a Cretaceous fossil in the Chalk-marl of Lemberg in Galicia ; and has been observed 
in several formations of Tertiary age, such as the Septaria-clay of Eikel, near Salzgitter, 
the Salt-clay of Wieliczka, and various Miocene deposits of the neighbourhood of 
Vienna. 
