EOEAMINIEEEA FEOM THE NOETH ATLANTIC AND AECTIC OCEANS. 
S81 
is masked in some degree" by the obesity of the chambers themselves ; the retinaculate 
variety developing smaller and more depressed lobes of sarcode. On Chamci gigas there 
is often a wild-growing parasitic Tinoporus isomorphous with PI. retinaculata, but still 
larger. 
The oldest known Planorbulince are found in the Lias. 
Planorbulina farctct, Fichtel and Moll, sp., Yar. ( Truncatulina ) lobatula, Walker and 
Jacob, sp. Plate XIV. figs. 3-6 (Arctic); Plate XVI. figs. 18-20 (North Atlantic). 
Planorbulina lobatula has been described above to some extent ; we may add that it 
is an exceedingly unstable form, even whilst keeping its simple character ; for frequently 
it has only half the thickness seen in fig. 5 b, which is an average specimen for such as 
live at from 30 to 160 fathoms in the Northern Seas; but at about 60 to 70 fathoms it 
frequently assumes a modified condition, taking a high conical shape ( PI . refulgens, Mont- 
fort, sp.), its smoothness and polish being much greater than in these flatter forms ; and 
the apex of the shell is on the umbilical aspect (as in PI. lobatula) ; the whole coil of 
chambers being seen on the base of the shell. PI. lobatula also passes insensibly into 
an extremely thin scale-like variety, nearly symmetrical, with limbate septal lines and 
square edges, which has been described as Planulina Ariminensis , D’Orb. (Modeles, 
No. 49). Other forms gradually lose the plano-convex, or Truncatuline, character ; the 
edges become rounded, the primary and succeeding chambers become elevated above 
the margin of the shell, which thus grows biconvex or lenticular; for instance, Pla- 
norbulina Haidmgerii, D’Orb., sp. (For. Foss. Vien. pi. 8. figs. 7-9), and PL Ungerianci , 
D’Orb., sp. (Ibid. figs. 16-18), common forms at from 60 to 300 fathoms. We here 
omit any notice of the intermediate varieties, which have been extensively named as 
species. 
Like Pulvinulina repanda , as seen in its variety P. Micheliniana (Plate XIV. fig. 16), 
the Truncatuline forms of PI. farcta have the spiral arrangement of the chambers 
marked on the flat face of the shell ; on the other hand, the plano-convex varieties of 
Discorbina Turbo have the umbilical surface flat ; the apex of the cone being formed of 
the primordial chamber : an approach to this condition is seen in Plate XIV. figs. 18, 19, 
Discorbina obtusa , D’Orb., sp. (For. Foss. Vien. pi. 11. figs. 4-6), a variety of D. Turbo , 
D’Orb., sp. (Modeles, No. 73). 
Plate XIV. figs. 3-6 represent specimens of PI. lobatula from the Hunde Islands, in 
five dredgings by Dr. P. C. Sutherland (25 to 70 fathoms), where they are very common 
and generally of good size; from Baffin’s Bay, at three places; lat. 75° 10' N., long. 
60° 12' W., and lat. 76° 30' N., long. 77° 52' W., of middling size and common, and at 
lat. 75° N., long. 59° 40' W. (220 fathoms), where they are small and rather common; 
and from seven out of the eight dredgings by Mac Andrew and Barrett on the Nor- 
wegian coast we have them large and common. We have already indicated that this 
variety is world-wide ; fossil, it occurs in the Chalk-marl, Chalk, and many later deposits. 
Fig. 6 shows a condition of the parasitic forms of Planorbulina farcta very common, 
mdccclxv. 3 f 
