600 
THE VOYAGE OF H.M.S. CHALLENGER. 
Islands, in the Eastern Archipelago, depth 580 fathoms, the only point at which the 
species has been found in any abundance. 
Globigerina pachyderma, Ehrenberg, sp. (PL CXIY. figs. 19, 20). 
Aristerospira pachyderma, Ehrenberg, 1873, Abhandl. d. k. Akad. Wiss. Berlin [1872], p. 386, 
pi. i. fig. 4. 
„ crassa, Id. Ibid. p. 388, pL iii. fig. 9. 
Globigerina omphalotetras, Id. Ibid. p. 388, pi. iii. fig. 11. 
„ bulloides, “arctic variety,” Brady, 1878, Ann. and Mag. Nat. Hist., ser. 5, vol. i. 
p. 435, pl.xxi. fig. 10, a-c. 
„ bulloides, var. borealis, Id. 1882, Proc. Roy. Soc. Edin., vol. xi. p. 716. 
Test Eotaliform, subglobular, more or less compressed, peripheral edge rounded ; 
formed of two convolutions, of which the outermost consists of four relatively large 
chambers ; segmentation obscure externally, the sutures being very slightly depressed ; 
aperture an arched or semicircular fissure at the margin of the final segment on its in- 
ferior side. Diameter, -^gth inch (0*3 mm.). 
The small thick-shelled Globigerina common in cold areas, if not peculiar to them, 
appears to have been first named by Ehrenberg (loc. cit.), from specimens collected in 
Davis Strait, — a fact which I had previously overlooked, owing to the method pursued 
by the veteran German histologist of making his drawings from balsam-mounted shells, 
by transmitted light. 
Under the name Globigerina bulloides, var. borealis, this form was noticed in 
the following terms : — “ The test is of smaller dimensions than that of Globigerina 
dutertrei, the longer diameter of fully-grown specimens being about 0'3 mm. (that of the 
d’Orbignian species being 0’5 mm.), and it has fewer chambers, almost invariably four in 
the final convolution. The shell- wall is relatively much thicker and the aperture less 
conspicuous, but the habit of growth in other respects is very similar. Compared with 
Globigerina bulloides, the shell is more compactly built, its segments are less inflated 
and globular, and it has no umbilical vestibule” (“Knight Errant” Eeport, loc. cit.). As 
in the other thick-shelled varieties of the genus, the walls of the test are very distinctly per- 
forated, but the actual diameter of the pore-canals does not exceed inch (0'0025 
mm.). 
As already stated, Globigerina 'pachyderma is peculiar to high latitudes. The most 
southerly point at which it has been observed is the “cold area” of the Faroe Channel, in 
about lat. 60° N. Within the Arctic Circle it is the most common representative of 
the genus, occurring sometimes alone and sometimes in company with small specimens 
of Globigerina bulloides. I have never succeeded in finding it in the tow-net gatherings, 
although small examples of the typical Globigerina bulloides are not uncommon amongst 
the surface organisms of the same areas. 
