374 
THE VOYAGE OF H.M.S. CHALLENGER. 
The Textularian segments are a good deal arched, the curvature of the earlier ones being 
sometimes sufficient to give a distinctly spiral arrangement to the commencement of the 
shell. This feature, which is shown in the specimen represented in Pl. XLV. fig. 7, is 
well illustrated by Batsch in his sectional drawing (loc. cit., fig. 13 d ). 
The geographical distribution of Bigenerina pennatula is practically the same as that 
of Bigenerina capreolus, with which it is generally found associated ; and the geological 
range of the two species appears to be nearly coincident. 
Pavonina, d’Orbigny. 
Pavonina, d’Orbigny [1826], Bronn, Brady, Moebius. 
The genus Pavonina was originally described in the Tableau Mdthodique, in which 
it was placed at the end of the Family Stichostegues, the multiple aperture, depressed 
test, and concentric chambers being given as the distinctive characters. Comparatively 
recently it has been shown that the test is in reality dimorphous, and that only the later 
segments are disposed concentrically, the earlier ones being alternate and Textularian. 
Our knowledge of the type is confined to a single species. 
Pavonina fiabelliformis, d’Orbigny (PI. XLV. figs. 17-21). 
Pavonina fiabelliformis, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 260, No. 1, pl. x. 
figs. 10, 11. — Modele, No. 56. 
,, „ Brady, 1879, Quart. Journ. Micr. Sci., vol. xix., N. S., p. 68, pl. viii. 
figs. 29, 30. 
„ ,, Moebius, 1880, Foram. von Mauritius, p. 91, pl. viii. figs. 11, 12. 
The test of Pavonina fiabelliformis is complanate and spreading, and except for 
some thickening of the earlier portion, the two faces are nearly flat; the general outline 
is fan-shaped or reniform. The early segments are small and arranged alternately as in 
Textularia. The later segments are narrow and much arched, and are disposed in single 
series ; they extend from one lateral margin to the other, and increasing rapidly in 
length give the test its fan-like contour. The shell- wall is thin and transparent, the 
perforations numerous and large, and often arranged in two or three irregular rows on 
the lateral faces of each segment ; and the sutures are limbate externally. The general 
aperture consists either of a single row of rounded orifices on the septal plane of the 
final segment (fig. 20), or of a larger number of smaller pores disposed in regular lines 
(as in Moebius’ drawings, op. cit.), or irregularly (fig. 21). When the apertural pore- 
canals are minute, they are somewhat prolonged outwards in the form of short 
delicate projecting tubes (Moebius, pl. viii. figs. 13 r, 14 r) ; but when the orifices 
are of larger size and in single row, the edges are only thickened sufficiently to form 
