ON THE GENUS POLYMORPHINA. 249: 
as extreme examples of the normal arrangement, inasmuch as they do not exhibit 
any real differenee of plan between the earlier- and later-formed portions of the shell. 
The phenomenon of change in the typical plan of growth is by no means uncommon 
amongst the Foraminifera. A triserial genus may have biserial varieties; for instance, 
Bulimina, which in all its more perfect forms has three or more segments to each 
turn of its'spire, presents in the feebler varieties which constitute the subgenus Boli- 
vina, an alternation of but two sets of chambers, and in this condition is scarcely 
distinguishable from Textularia ; whilst Textularia itself, though typically biserial, 
has a uniserial group (Bigenerina) precisely analogous to the Polymorphine subgenus 
Dimorphina. The closely allied genus Uvigerina has also a uniserial section, described: 
by D'Orbigny under the generic name Sagrina; and it would be very difficult to assign 
any characters that would serve in every case to distinguish it from Dimorphina. The 
Uvigerine parentage generally, however, betrays itself either in a long phial-shaped neck 
or by an ornamentation of raised lines and minute spines at some portion of the surface 
of the test. ! 
Distribution.—1t is to its morphological peculiarities, and to the assistance they yield 
in elucidating the relationship of several parallel genera, that Dimorphina owes its 
interest and importance; for in point of distribution the subgenus yields little ground 
for comment. Itis very rare both in a recent and fossil state, too rare to be of service 
in the estimation of any external physical conditions. Its occurrence seems to be limited 
to a few particular deposits of the Tertiary epoch and to occasional living specimens from 
the seas of warm latitudes. 
DIMORPHINA TUBEROSA, D'Orbigny *. (Plate XLII. figs. 39, a, b.) 
Orthoceratium tuberosum, Soldani, 1780, Testac. ac Zooph. vol. ii. p. 99, pl. 106. fig. gg. 
Dimorphina tuberosa, D'Orbigny, 1826, Ann. Sci. Nat. vol. vii. p. 264, No. 1; “ Modele,” No. 60. 
D. nodosaria, D'Orbigny, 1846, For. Fos. Vien. p. 221, pl. 12. figs. 21, 22. 
D. tuberosa, Parker, Jones, & Brady, 1865, Ann. & Mag. Nat. Hist. 3 ser. vol. xvi. p. 14, pl. 2. fig. 53. 
D. nodosaria (in part), lid. 1866, Monogr. Crag Foram., App. I. & 11. pl. 1. fig. 61; Karrer, 1868, Sitzungs. 
k. Akad. Wissenschaft, vol. lviii. p. 177. 
Characters.—Shell elongate, subcylindrical, straight, or nearly so. Anterior portion 
acuminate; posterior obtuse, and rounded. Early (alternating) chambers varying greatly 
in their proportion to the whole shell. Later (uniserial) chambers two to six in number, 
more or less inflated. Surface smooth. Length 3 to #5 inch. | 
The differences indicated by M. D'Orbigny between Dimorphina tuberosa and D. no- 
dosaria are such as will scarcely bear examination ; and we are compelled to regard them 
as the same variety, reserving the latter trivial name for a distinct unciae to the 
Polymorphine proper, described by Professor Reuss. M. D'Orbigny's figures of the 
* It is the custom to ignore the names given by pre-Linnwan observers, and those who wrote before the Linnean 
method of nomenclature was generally adopted, in quoting the authority for specific or generic terms; else to Soldani, 
rather than D’Orbigny, should the present species be attributed; the latter only adopted the designation previously 
given by TS TOME SE. | fatig 1. m a dins di 
Tot 
