REPORT ON THE FORAMLNTFERA. 
661 
show the calcareous shell within. When the contour of the sandy envelope is regular and 
convex, as in the former case, the specimens may easily he mistaken at first sight for 
Webbina hemisphcerica, though always distinguishable by the different mode of aggrega- 
tion of the sand-grains, which in the present species are retained in their position chiefly, 
if not entirely, by the sarcode of the living animal, whilst in Webbina they are 
embedded in inorganic cement and form a compact wall. A similar tendency to form a 
protective rampart of sand is noticeable in certain other species of adherent Foraminifera, 
notably in some arenaceous or subarenaceous types, such as Valvulina, but seldom to the 
extent of providing a complete covering. 
Truncatulina lobatula is common at every latitude, from the most northerly points of 
the Arctic Ocean yet explored to the Antarctic Ice-barrier. Bathymetrically speaking, it 
is most abundant in the littoral, laminarian, and coralline zones, but it is by no means 
confined to shallow bottoms, and is still conspicuous at depths of nearly 3000 fathoms. 
Its geological distribution is also very extensive. Specimens of the compact variety 
have been met with in rocks of Carboniferous age ; and shells indistinguishable from 
those living at the present day on our own shores are found in the later Mesozoic 
formations, and in almost every marine deposit of Tertiary and Post-tertiary times. 
Truncatulina variabilis, d’Orbigny (PI. XCIII. figs. 6, 7). 
“Teste hammoniformes, plano-cochleatce, tuberoses articulates, &c.,” Soldani, 1789, Testaceo- 
graphia, vol. i. pt. 1, pp. 77-80, pis. lxx.-xcii. 
Truncatulina variabilis, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 279, No. 8. 
„ innormalis, Costa, 1856, Atti dell’ Accad. Pont., vol. vii. p. 368, pi. xxi. fig. 11. 
Planorbulina truncata, Egger, 1857, Neues Jahrb. fur Min., &c., p. 280, pi. x. figs. 15-17. 
Truncatulina tuberosa, Parker, Jones, and Brady, 1871, Ann. and Mag. Nat. Hist., ser. 4, 
vol. viii. p. 177, pi. xii. fig. 138. 
„ variabilis , Terquem, 1878, Mem. Soc. geol. France, ser. 3, vol. i., Mem. Ill, p. 20, 
pi. i. figs. 18-25. 
The wild-growing adherent Truncatulina, to which Soldani devotes upwards of twenty 
plates of the “ Testaceographia,” without exhausting their multiform aspects, are grouped 
by d’Orbigny under a single specific name, Truncatulina variabilis. 
Such varieties occur in greater or less numbers wherever the more normally 
constructed shells are at all abundant, but they are commonest at the shallow margins of 
subtropical and temperate seas. They are not, however, entirely confined to shallow water, 
for occasional specimens have been met with at depths of 500 or 600 fathoms, and in one 
instance at upwards of 2000 fathoms. 
As a fossil Truncatulina variabilis has probably a similar range to Truncatulina 
lobatula, though there appears to be no mention of its occurrence in any formation 
earlier than the Eocene of the Paris Basin (Terquem). It has been obtained from the 
(ZOOL. CHALL. EXP. PART XXII. 1884.) ^ ^4 
