222 
THE YOYAGE OF H.M.S. CHALLENGER. 
In point of internal structure the genus furnishes examples of two somewhat distinct 
modes of growth corresponding to the simple and complex types of Orbitolites. In the 
simple type, to which the small, spheroidal, recent form and most of the fossil species 
pertain, the long arched chambers are divided by vertical septa into chamberlets, and the 
normal aperture consists of a line of bordered pores on the outer face of the terminal 
segment, corresponding in number to the chamberlets into which the segment is partitioned. 
Occasionally there is a second or accessory row of smaller pores. This simple type is 
easily understood by its analogy to a nautiloid Orbiculina drawn out at the two umbilici. 
In the complex type, of which the common recent Alveolina boscii furnishes the best 
example, the chambers are not only divided by vertical septa, as before described, but the 
individual chamberlets are subdivided by horizontal partitions into a number of parallel 
layers or storeys ; and, instead of a single row of orifices, the face of the terminal segment 
is studded with numerous pores, disposed in more or less regular lines corresponding 
with the subdivisions of the chamber-cavities. A comparison of the longitudinal and 
transverse sections (PI. XVII. figs. 14, 15, with figs. 11, 12), or still better, a reference 
to Dr. Carpenter’s larger and more diagrammatic drawings, will show at a glance the dis- 
tinctive features of the two types of structure. 
Carter has described a Tertiary form, Alveolina mtfandrina, the shell of which exhibits 
traces of a canal system in the early stages of growth; but he suggests at the same time 
that the species is probably more nearly related to Nummulites than to Alveolina } 
So far as at present known, the geographical distribution of the genus is limited to the 
shallow water of tropical seas, and in such localities it is abundant and widely diffused. 
From a geological point of view, Alveolina is best known by its Tertiary representa- 
tives ; nevertheless d’Orbigny, in the Prodrome de Paleontologie, enumerates two species 
from the Cenomanian or Middle Cretaceous rocks of the south of France, and one from 
the Turonian or Upper Cretaceous beds of the same or an adjoining region. Fossil 
specimens are found in some abundance in the Nummulitic Limestones of France 
(Pyrenees), Spain, Persia, and Northern India ; in the Eocene beds of the neighbourhood 
of Paris and of the south of England (Bracklesham), and in the Miocene of various parts 
of Austria and Transylvania. 
Alveolina boscii, Defrance, sp. (PI. XVII. figs. 7-12). 
Alveolites larva, (?) Defrance, 1816, Diet. Sci. Nat., vol. i. p. 137. 
Oryzaria boscii, Id. 1820, Ibid. vol. xvi. p. 104. 
Alveolina boscii, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 306, No. 5; — Module, No. 50. 
„ elongata, Id. Ibid. p. 307, No. 6. 
„ quoii, Id. Ibid. p. 307, No. 7. 
,, longa, Czjzek, 1847, Haidinger’s Nat. Abbandl., vol. ii. p. 143, pi. xii. figs. 34, 35. 
„ boscii, Moebius, 1880, Foram. Mauritius, p. 79, pi. iii. figs. 13-15; pi. iv. fig. 1. 
1 Ann. and Mag. Nat. Hist., 1861, ser. 3, vol. viii. p. 381, pi. xvii. fig. 4. 
