380 
ME. W. K. PAEKEE AND PEOEESSOE T. E. JONES ON SOME 
Figs. 3 to 11 include two striking varieties of Planorbulina far eta, — a type perhaps 
the richest of all the Rotalines in modification; and which not only developes the 
largest chambers, but produces the largest shells (some with a diameter of a quarter of 
an inch, P. vulgaris, D’Orb.). The disk and the chambers are so large in some speci- 
mens from tropical seas, that individuals have been mistaken for Polyzoa, and this 
mistake has been strengthened by the pouting of the marginal apertures. 
Both of the varieties here under consideration, though attaining considerable size, are 
arrested and few-chambered varieties. They have attained the simple Rotaline form 
without as yet taking on the more characteristic features of the more outspread Planor- 
bulince, although their somewhat free mode of growth, the coarseness of their shell-walls, 
and their relatively large aperture afford the connecting links to the observer ; more 
especially when we find the same shells having the aperture firstly lipped, then pro- 
trusive, and gradually (among numbers of individuals) acquiring a neck and distinct 
rim. The typical development of this Planorbulina, with a subtubular chief aperture 
and supernumerary necked and lipped apertures on the periphery of the shell, is rarely 
found in the northern seas ; by far the most common variety is the well-known form, 
figs. 3-6, long ago described as Truncatulina lobatula. This, as a rule, grows on a 
shell or other substance having a smooth surface, and during the growth of the shell 
the little parasitical Foraminifer occasionally becomes more or less imbedded in its 
substance. This plano-convex variety represents in the temperate climes the many- 
chambered plano-convex Planorbulina Mediterranensis. The latter swarms on sea- 
weeds and shells in the shallow water of the Mediterranean ; and it is in company with 
it (especially when growing on the larger bivalves, such as Pinna fiabellum ) that PI. 
lobatula is seen to take on a wild-growing condition, with subsidiary marginal necks, 
becoming PI. farcta and PI. variabilis , without developing nearly so many chambers as 
are seen in its associate, although exceeding the latter in size. In tropical and sub- 
tropical seas PI. farcta grows on to be the great PI. vulgaris, D’Orb., the arrested 
Truncatuline forms being comparatively rare. 
In the seas of hot climates a large amount of exogenous granular matter is formed 
o o o 
on the surface of the shell (as in PL larvata *, Parker and Jones); far different to the 
smooth, polished shells in the Mediterranean and northern seas. There is one parasi- 
tical form (PI. retinaculataf , Parker and Jones) which, besides being scabrous with gra- 
nulation, developes so large a number of peripheral, subsidiary, tubular apertures, con- 
necting together, and still keeping apart, the sarcode-chambers, and forming a kind of 
irregular network over the surface of the shells on which it grows, like certain Polyzoa, 
that the features of this Planorbulina are extremely different from that of its type ; and 
it can scarcely be connected with the simple varieties of the species without a know- 
ledge of the real relationships of the great and widely extended Rotaline group. The 
same structure really exists in the great Pl. vulgaris, D’Orb. For. Canar. pi. 2. fig. 30, 
and Carpenter, Introd. For. pl. 13. figs. 13-15 ; but here the connexion of the chambers 
* Plate XIX. fig. 3. Ann. Nat. Hist. 3 ser. vol. v. p. 68. 
f Plate XIX. fig. 2. Carpenter's Introd. Poram. p. 209. 
