FORAMINIFERA FROM THE NORTH ATLANTIC AND ARCTIC OCEANS. 379 
special names, which we must in many instances retain for convenience, though, we refer 
them to one or the other of the six species above mentioned. 
In nature these Foraminifera are never absolutely strict in their adherence to any one 
of the chief varietal forms ; but the latter are serviceable as subspecific centres, around 
which may be arranged a large number of modifications, more and more gentle and 
mutually confluent ; so that when we speak of Truncatulina lobatula or of Discorbina 
vesiculciris (and the same may be said of the varietal groups of any true Foraminiferal 
species), we do not mean to say that the specimen which we have before us necessarily 
answers exactly to any figure or description in the literature of the subject, but that it 
is nearer to some one of the accepted illustrations than to any other. To attempt greater 
exactness would be useless; indeed the classification of these little creatures is very 
similar to what that of vegetables would be if we had only the separate leaves for our 
guides. 
From 100 fathoms to shallow water (seaweed-belt, 10 fathoms and less) is the best 
home for the Rotaliform Rot almas. Certain varieties of Pulvinulina repanda attain a 
good size at 2400 fathoms. The varieties of Planorbulina farcta, also, are not uncom- 
mon at very great depths. Piscorbina Turbo , Rotalia Beccarii , Calcarina Spengleri , and 
Cymbalopora Poyei avoid great depths (with few exceptions), the best developed specimens 
keeping themselves above the Coralline-zone or 25 fathoms. 
Planorbulina has a coarsely porous shell (more so than any of its congeners), often of 
a relatively large size, consisting of from 15 to 200 or more chambers, with single septa, 
and very slight rudiments of the canal-system : it is usually complanate (PI. Mediterrci- 
nensis ) and parasitic on sea-weeds and shells ; but many of its varieties are plano-convex 
( Truncatulina ), and some become almost subnautiloid (Anomalina). The shell is mostly 
smooth ; rarely limbate ( Planulina ) ; and frequently granulate (PI. vulgaris and PI. 
larvata) : the aperture varies from an open to a contracted slit, and is often produced 
and lipped. 
Scheme of the chief members of the Rotaline genus Planorbulina. 
Fully developed forms ; 
Becoming concentric, with | 
alternating chambers < 
' • p 
built over the apertures of 
the penultimate ring. 
Intermediate for ma . 
Quasi-rotalian and 
subnautiloid forms. • ' 
vulgaris, D’Orb. For. Foss. Canar. pi. 2. fig. 30; Carpenter, Introd. For. pi. 13. 
figs. 13-15. 
Mediterranensis, D’Orb. Modeles, No. 79. 
retinaculata, Parker and Jones (sp. nov.) ; Carp. Int. For. p. 209. Plate SIX. fig. 2. 
larvata, P. and J. (sp. n.), Ann. Nat. Hist. 3 ser. vol. v. p. 68. Plate SIX. fig. 3. 
farcta, Fichtel and Moll, sp. (the type of Planorbulina), Test, Micr. pi. 9. figs. g-i. 
lobatula ( Truncatulina ), Walker and Jacob, sp., D’Orbigny’s Modeles, No. 37. 
refulgens, Montfort, sp., D’Orbigny’s Modeles, No. 77. 
Haidingerii, D’Orb , sp., For. Foss. Yien. pi. 8. figs. 7-9. 
TJngeriana, D’Orb., sp., For. Foss. Yien. pi. 8. figs. 16-18. 
ammonoides, Reuss, sp., Bohm. Kreid. pi. 8. fig. 53. 
reticulata, Czjzek, sp., Hauling. Abhandl. ii. pi. 13. figs. 7-9. 
cor onata {Anomalina), Parker and Jones, Ann. Nat. Hist. 2 ser. vol. xix. p. 294, 
pi. 10. figs. 15, 16. 
Ariminensis ( Planulina ), D’Orb., sp., Modeles, No. 49-. 
