210 MESSRS. BRADY, PARKER, AND JONES 
There is, however, one set of forms, misunderstood by D'Orbigny, and correspondingly 
misplaced, which seems better entitled to the position of a subgenus or subtype, viz. 
those constituting his genus Dimorphina. All the biserial genera of Foraminifera have 
amongst their modifications some which show a tendency to a uniserial arrangement of 
a portion of their segments. In Textularia, for instance, there are a number of varieties, 
separated under the subgeneric name Bigenerina, differing in many of their characters, 
but alike in this—namely, that after the first few chambers have been formed on the 
normal alternating plan, the shell is completed by a uniserial line of segments. In the 
same way rare specimens of the Polymorphine type are found, in which the early seg- 
ments are triserial, or obscurely spiral, and the later ones assume a uniserial arrangement. 
Thus Dimorphina, the subgenus embracing these varieties, bears precisely the same rela- 
tion to Polymorphina that Bigenerina does to Textularia. These peculiar forms are in- 
teresting as supplying one of many evidences of the near relationship of the genus to 
the Nodosarinæ. In a large proportion of the specimens the later chambers are as com- 
‘pletely Nodosarian in character as the earlier ones are Polymorphine ; indeed it is an open 
question regarding such forms as the Dimorphina obliqua of: D'Orbigny, which of the two 
genera they are best assigned to. 
The genus Uvigerina, which is normally triserial, supplies another such instance in its 
subgenus Sagrina; and the resemblance its uniserial specimens often bear to those of 
Dimorphina is so close that the produced phial-shaped neck and lip is almost the only 
character which determines their Uvigerine affinity. Herr Schwager, in his contribution 
to the geological part of the * Novara-Reise, figures a beautiful variety of this kind as 
Dimorphina striata, which we have reluctantly omitted, regarding it as a striate Sagrina, 
on the ground of its neatly formed Uvigerine neck. — . 
Accepting the shell first figured by Walker and Boys*, the smooth, hyaline, Globuline 
form named by them Serpula lactea, as the type of the genus, it is easy to divide the 
Polymorphine proper into two groups,—1st, those having smooth shells, and, 2ndly, 
those having tests more or less altered by outgrowths of shell-substance, constituting a 
sort of surface-ornamentation. But, broad and well defined as this division seems, it is 
by no means absolute; for perfectly smooth examples of Polymorphina Jrondiformis may 
frequently be met with, although it is necessarily placed amongst the “ornamented.” 
forms on account of the subcostate surface of the majority of specimens. _ 
lst. Of the smooth varieties little need be said in explanation of the order which has 
been adopted in the treatment of the species. Two somewhat anomalous forms, P. con- 
cava, Williamson, and P. Humboldti, Bornemann, whose plano-convex shape appears 
to be due to a parasitic habit of growth t, are placed at the end of the series; and another - 
interesting modification, P. elegantissima, Parker and Jones, is equally removed from the 
normal type by the reversed direction of its later segments. But beyond these excep- 
* * Testacea minuta rariora, &c., p. 2, pl. 1. fig. 5. 
t For P. Humboldtii this character is assumed from analogy, and we lay no stress upon it, never having seen spe- 
cimens exactly similar to those figured by Dr. Bornemann; but whether our supposition be correct or not, the en 
assigned to it is probably nearly its natural one, is vr E In ass i 
