546 
THE VOYAGE OF H.M.S. CHALLENGER. 
Cristellaria convergent, Bornemann (PL LXIX. figs. 6,7). 
Cristellaria convergens, Bornemann, 1855, Zeitschr. d. deutsch. geol. Gesellsch., vol. vii. p. 327, 
pi. xiii. figs. 16, 17. 
„ elliptica, Id. Ibid. p. 328, pi. xiii. fig. 18. 
The test of Cristellaria convergens is oval and biconvex, its peripheral edge is sharp 
but non-carinate, and the terminal segment is drawn out to a point at the apertural end. 
The species is distinguished from its congeners by the peculiar shape of the segments, the 
two outer lateral edges of which are drawn together so as to leave an extremely narrow 
septal face. The septation is very obscure, often scarcely visible externally, owing to the 
thickening of the walls by the extension of the alar flaps of the chambers over the sides 
of the shell. It is to the convergence of the edges of the final segment and the embrac- 
ing nature of the chambers that the characteristic outline of the shell is due. 
The best specimens of Cristellaria convergens, and those with thickest walls, have all 
been taken from very deep bottoms ; and it is possible that the form may only represent a 
deep-water variety of Cristellaria gibba, or some such species, though it appears to 
have well differentiated characters in its fully developed condition. 
This species has been found at four Stations in the North Atlantic, at depths ranging 
from 390 to 2740 fathoms; at one point in the South Atlantic, 2350 fathoms; at four 
in the South Pacific, 16 to 1375 fathoms ; and at one in the North Pacific, 1850 fathoms. 
The specimens originally described by Bornemann were Tertiary fossils, from the 
Septaria-clay of Hermsdorf near Berlin. 
\ 
Cristellaria gibba, d’Orbigny (PI. LXIX. figs. 8, 9). 
Cristellaria gibba, d’Orbigny, 1839, Foram. Cuba, p. 63, pi. vii. figs. 20, 21. 
,, excisa, Bornemann, 1855, Zeitscfir. d. deutsch. geol. Gesellsch., vol. vii. p. 328, 
pi. xiii. figs. 19, 20. 
„ nuda, Reuss, 1861, Sitzungsb. d. k. Ak. Wiss. Wien, vol. xliv. p. 328, pi. vi. 
figs. 1-3. 
„ pidchella, Id., 1862, Ibid. vol. xlvi. p. 71, pi. viii. 
fig. 1. 
Robulina concinna, Id., 1863, Ibid. vol. xlviii. p. 52, pi. v. 
fig. 58. 
Cristellaria gibba occupies an intermediate position as one of the transition forms 
connecting the elongate compressed Cristellaria crepidula with the symmetrical and 
lenticular Cristellaria rotulata. The test is oblong and biconvex, and differs from that of 
Cristellaria acutauricularis chiefly in its comparatively narrow septal face. 
These closely allied varieties of Cristellaria are so much associated in distribution that 
it is next to impossible to give an account of their individual geographical range. Notes 
have been preserved of the occurrence of Cristellaria gibba in the North Atlantic and the 
