164 
THE VOYAGE OF H.M.S. CHALLENGER. 
Miliolina trigonula, Lamarck, sp. (PI. III. figs. 14-16). 
Miliolites trigonula, Lamarck, 1804, Ann. du Mus., vol. v. p. 351, No. 3; — 1822, Anim. s. Vert., vol. 
vii. p. 612, No. 3. 
„ cor-anguinum, Id. 1804, Ann. du Mus., vol. v. p. 351, No. 2; — 1822, Anim. s. Vert. vol. vii. 
p. 612, No. 2. 
„ „ Blainville, 1825, Man. de Malac., p. 369, pi. iv. fig. 3, a. b. 
Triloculina trigonula, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 299, No. 1, pi. xvi. figs. 5-9 ; — 
Module, No. 93. 
,, globulus, Id. 1839, Foram. Amer. M4rid., p. 71, pi. ix. figs. 9, 10. 
„ austriaca, Id. 1846, For. Foss. Vien., p. 275, pi. xvi. figs. 25-27. 
Miliola austriaca, Egger, 1857, Neues Jahrb. fiir Min., &c., p. 271, pi. vi. figs. 4-6. 
Miliolina trigonula, Williamson, 1858, Rec. For. Gt. Br., p. 83, pi. vii. figs. 180-182. 
(1) Bilocidina lucernula, “ triloculine variety,” Schwager, 1866, Novara-Exped., Geol. Theil., vol. ii. 
p. 202, pi. iv. fig. 14, a.h. 
Miliola trigonula, Fischer, 1870, Actes Soc. Linn. Bordeaux, vol. xxvii. p. 386, No. 2. 
There are few members of the Milioline group so constant even in their minor 
characters as Miliolina trigonula . The shell is regularly Triloculine, subspherical or oblong, 
and nearly circular in end-view. Nevertheless, if a large series be collected, a few 
specimens will generally be found amongst them, like fig. 14 (PI. IIP), which by the 
comparatively small exposure of the third segment attest their near relationship with the 
Biloculince. A shell almost identical with this in form has been figured by Dr. Sell wager 
( loo . cit.) as a “ Triloculine variety of Bilocidina lucernula" ; and so far as parentage, in that 
particular case, is concerned, there is no reason to question the diagnosis of so careful 
an observer ; but had the specimen occurred alone, it would probably have been assigned 
to the present species. 
On the other hand, the separation of Miliolina trigonula from Miliolina tricarinata 
depends solely on the comparative roundness or angularity of the three salient chamber- 
margins ; and, as this is of necessity an exceedingly variable character, there are often 
to be found intermediate specimens whose affinity must be judged by the forms with 
which they are associated rather than by their own individual peculiarities. 
Miliolina trigonula is a very widely distributed inshore species, more abundant 
in the temperate zones than in the tropics, but never reaching the polar seas. It is 
common at every part of our own coast. It has been collected at depths as great as 2300 
fathoms, but well-marked specimens are rare in deep water, and beyond 100 fathoms the 
species is generally replaced by Miliolina tricarinata. 
Its geological range extends throughout the Tertiary epoch. It occurs in the Eocene 
of the neighbourhood of Paris (Lamarck, d’Orbigny), in the Miocene of Austria and Lower 
Bavaria (d’Orbigny, Egger), in the Pliocene of many localities in Italy (Jones and Parker), 
and in the Post-tertiary beds of the West of Scotland (Robertson) and of North of 
Ireland (Stewart). 
